JAMB UTME - Chemistry - 2025

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Tristearin is a fat (triglyceride) formed from glycerol and three molecules of stearic acid. Alkaline hydrolysis of a triglyceride is the reaction of the fat with a strong alkali such as sodium hydroxide. This reaction is known as saponification and produces soap (the sodium salt of the fatty acid) and glycerol as a by-product:

\[\text{(C}_{17}\text{H}_{35}\text{COO)}_3\text{C}_3\text{H}_5 + 3\text{NaOH} \rightarrow 3\text{C}_{17}\text{H}_{35}\text{COONa} + \text{C}_3\text{H}_5\text{(OH)}_3\]

The by-product is glycerol, also known as propane-1,2,3-triol. Its structural formula shows three hydroxyl (-OH) groups, one on each of the three carbon atoms. An alcohol with three -OH groups is classified as a trihydric alkanol.

A dihydric alkanol has two -OH groups (e.g. ethane-1,2-diol). A secondary alkanol has the -OH group on a carbon bonded to two other carbon atoms. A tertiary alkanol has the -OH on a carbon bonded to three other carbons. Glycerol has two primary -OH groups and one secondary -OH group, but its defining classification is that it is trihydric, since it carries three hydroxyl groups in total.

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The number of molecules in a sample is found by multiplying the number of moles by Avogadro's number. The relationship is:

\[N = n \times N_A\]

where \(N\) is the number of molecules, \(n\) is the number of moles, and \(N_A\) is Avogadro's number (\(6.02 \times 10^{23}\)).

Substituting the given values:

\[N = 4.0 \times 6.02 \times 10^{23}\]

\[N = 24.08 \times 10^{23}\]

\[N = 2.408 \times 10^{24}\]

Rounding to three significant figures gives \(2.41 \times 10^{24}\) molecules.

A common error is dividing instead of multiplying. Dividing 6.02 by 4 would give \(1.51 \times 10^{23}\), which is the number of molecules in 0.25 moles, not 4.0 moles. When you have more than one mole, the number of molecules must be greater than Avogadro's number, so any answer smaller than \(6.02 \times 10^{23}\) can be immediately ruled out.

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Producer gas is a mixture of carbon monoxide (CO) and nitrogen (N₂), while water gas is a mixture of carbon monoxide (CO) and hydrogen (H₂). Both gases contain CO, which is toxic and must be removed for certain industrial applications.

Ammoniacal copper(I) chloride solution (CuCl dissolved in ammonia) is the reagent used to selectively absorb CO from these gas mixtures. The CO molecules form a coordination complex with the copper(I) ions in solution:

\[ \text{CuCl} + \text{CO} + 2\text{NH}_3 \rightarrow [\text{Cu(CO)(NH}_3\text{)}_2]\text{Cl} \]

This reaction is reversible: gentle heating releases the absorbed CO and regenerates the ammoniacal CuCl solution for reuse.

The other gases in these mixtures are not absorbed by this reagent. Hydrogen (H₂) does not form stable complexes with Cu⁺ under these conditions. Nitrogen (N₂) is chemically inert at room temperature. Carbon dioxide (CO₂) would be absorbed by alkaline solutions such as NaOH or KOH, not by ammoniacal CuCl.

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Water has an unusually high boiling point (100 °C) for a molecule of its small size (relative molecular mass = 18). To understand why, compare water (H₂O) with hydrogen sulphide (H₂S), which has a larger relative molecular mass of 34 but is a gas at room temperature (boiling point -60 °C). The difference lies in the type of intermolecular forces present.

Each water molecule can form up to four hydrogen bonds with neighbouring molecules. Oxygen is highly electronegative, creating a large partial positive charge on the hydrogen atoms. These hydrogen atoms are attracted to the lone pairs on the oxygen of adjacent water molecules, forming strong intermolecular hydrogen bonds. This extensive hydrogen-bonding network requires a large amount of energy to break, which raises the boiling point far above what the molecular mass alone would predict.

The covalent bonds within each water molecule (O-H bonds) hold the atoms together inside one molecule, but they do not determine the physical state. Van der Waals forces are present in all molecules but are too weak on their own to keep such a light molecule in the liquid state at room temperature. Electrovalent (ionic) bonds do not exist in water, which is a covalent molecular substance.

It is therefore the strong hydrogen bonding between water molecules that keeps water liquid at room temperature.

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The spontaneity of a reaction is determined by the Gibbs free energy change, given by:

\[\Delta G = \Delta H - T\Delta S\]

A reaction is spontaneous when \(\Delta G\) is negative.

In this question:

• \(\Delta H\) is positive and small (slightly endothermic).
• \(\Delta S\) is positive and large (significant increase in disorder).

Substituting into the equation:

\[\Delta G = (\text{small positive}) - T \times (\text{large positive})\]

Since \(T\) (absolute temperature in Kelvin) is always positive, the term \(T\Delta S\) will be a large positive number. Subtracting this large positive value from a small positive \(\Delta H\) gives:

\[\Delta G = \text{small positive} - \text{large positive} = \text{negative}\]

A negative \(\Delta G\) means the reaction is spontaneous.

Exam tip: When \(\Delta H\) is positive but \(\Delta S\) is also positive and large, the entropy term dominates, and the reaction is spontaneous, especially at higher temperatures. This is called an entropy-driven reaction.

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Transition metals are widely used as catalysts in both industrial and biological processes. The key electronic property that makes them effective catalysts is the presence of partially filled d-orbitals.

Partially filled d-orbitals allow transition metals to:

• Exhibit variable oxidation states by losing different numbers of d-electrons, enabling them to participate in electron-transfer steps during a reaction.
• Form temporary bonds with reactant molecules by accepting or donating electron density through their available d-orbitals, which lowers the activation energy of the reaction.
• Provide a suitable surface or coordination environment for reactants to adsorb, orient, and react more readily.

A filled d-orbital would mean the metal has no vacant d-orbitals to accept electron density from reactants, greatly reducing its catalytic ability. Similarly, f-orbitals (whether filled or partially filled) are associated with the inner transition metals (lanthanides and actinides) and are not the primary reason for catalytic activity in the common transition metal catalysts such as iron, nickel, platinum, and palladium.

Exam tip: The two key properties of transition metals to remember are variable oxidation states and catalytic activity, both arising from partially filled d-orbitals.

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When solid particles such as dust and sand are dispersed in a gas (air), the resulting system is classified based on particle size and behaviour.

A suspension is a heterogeneous mixture in which relatively large, visible particles are dispersed in a medium. The particles in a suspension are large enough to eventually settle out under gravity and can often be seen with the naked eye. Dust and sand particles in air fit this description: they are large, they scatter light visibly, and they settle when the air is still.

The other options do not fit:

• An emulsion is a mixture of two immiscible liquids (such as oil in water). Dust in air does not involve two liquids.
• A saturated solution is a homogeneous mixture where no more solute can dissolve at a given temperature. Dust particles are not dissolved in air.
• A dispersion is a broad term for any system in which one substance is spread throughout another, but it does not specifically describe the large-particle, settling behaviour of dust and sand in air.

Because dust and sand particles are large, visible, and settle out over time, the system is best classified as a suspension.

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The molecular mass (molar mass) of a substance is defined as the mass of one mole of that substance. The relationship is:

\[\text{Molar mass} = \frac{\text{Mass}}{\text{Number of moles}}\]

Given that 0.5 mole of the alkanoic acid weighs 44 g:

\[\text{Molar mass} = \frac{44\,\text{g}}{0.5\,\text{mol}} = 88\,\text{g/mol}\]

The molecular mass of the alkanoic acid is therefore 88. This corresponds to butanoic acid (CH₃CH₂CH₂COOH), which has the molecular formula C₄H₈O₂: (4 x 12) + (8 x 1) + (2 x 16) = 48 + 8 + 32 = 88.

A common error is to multiply mass by moles instead of dividing. Remember: if a fraction of a mole has a certain mass, the full mole must weigh proportionally more.

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A water pollutant is any substance or condition that degrades the quality of a water body and harms aquatic life or makes the water unsuitable for its intended use.

Oxygen gas is not a water pollutant. In fact, dissolved oxygen is essential for aquatic life. Fish and other aquatic organisms depend on dissolved oxygen for respiration. A water body with adequate dissolved oxygen levels is considered healthy.

The other options are all recognised water pollutants:

• Warm water effluent (thermal pollution): Discharge of heated water from power plants or factories raises the temperature of natural water bodies, which reduces the solubility of dissolved oxygen and disrupts aquatic ecosystems.
• Inorganic fertilizers: Nitrates and phosphates from agricultural runoff cause eutrophication, leading to excessive algal growth, oxygen depletion, and death of aquatic organisms.
• Biodegradable waste: Organic matter such as sewage increases the biological oxygen demand (BOD) of the water, depleting dissolved oxygen as microorganisms decompose the waste.

Since oxygen gas is a natural and beneficial component of water, it is not classified as a pollutant.

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The corrosion of iron is specifically called rusting. Rusting occurs when iron reacts with oxygen and water (moisture) over time to form hydrated iron(III) oxide, commonly known as rust:

\[4\text{Fe} + 3\text{O}_2 + 6\text{H}_2\text{O} \rightarrow 4\text{Fe(OH)}_3\]

The iron(III) hydroxide gradually dehydrates to form the familiar reddish-brown rust (Fe₂O₃ . xH₂O). Both oxygen and water must be present for rusting to occur; iron does not rust in dry air or in air-free water.

The other options are different processes entirely: burning (combustion) is a rapid reaction with oxygen involving flame and heat; galvanizing is a method of preventing corrosion by coating iron with a layer of zinc; alloying is mixing metals together to form an alloy (such as stainless steel), which is also a corrosion-prevention strategy, not a corrosion process.

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The pH of a salt solution depends on the strength of the acid and base from which the salt was formed. A salt formed from a strong acid and a strong base produces a neutral solution with a pH of 7, because neither ion undergoes hydrolysis in water.

Sodium chloride (NaCl) is formed from hydrochloric acid (HCl, a strong acid) and sodium hydroxide (NaOH, a strong base). When dissolved in water, the Na⁺ and Cl^- ions do not react with water, so the solution remains neutral at pH 7.

The other salts behave differently:

• Ammonium chloride (NH₄Cl) is formed from a weak base (NH₃) and a strong acid (HCl). The ammonium ion hydrolyses in water to release H⁺ ions, making the solution acidic (pH below 7).
• Ammonium tetraoxosulphate(VI) ((NH₄)₂SO₄) is also formed from a weak base and a strong acid, producing an acidic solution.
• Sodium trioxocarbonate(IV) (Na₂CO₃) is formed from a strong base (NaOH) and a weak acid (H₂CO₃). The carbonate ion hydrolyses in water to produce OH^- ions, making the solution basic (pH above 7).

Exam tip: To predict the pH of a salt solution, identify the parent acid and base. Strong acid + strong base gives pH 7; strong acid + weak base gives pH below 7; weak acid + strong base gives pH above 7.

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Carbon(II) oxide is the IUPAC-style name for carbon monoxide (CO). It is a colourless, odourless, and highly toxic gas that is a major air pollutant, especially in urban areas.

The primary source of carbon monoxide as an air pollutant is the incomplete combustion of carbon-containing fuels. When fuels such as petrol, diesel, kerosene, coal, or wood burn with an insufficient supply of oxygen, carbon is only partially oxidised to CO instead of fully oxidised to CO₂:

\[ 2\text{C} + \text{O}_2 \rightarrow 2\text{CO} \]

Vehicle exhaust emissions are the single largest contributor of CO to the atmosphere, along with industrial furnaces and domestic cooking fires that operate under oxygen-poor conditions.

Respiration produces carbon dioxide (CO₂), not carbon monoxide. Photochemical smog is a secondary pollution phenomenon caused by sunlight acting on nitrogen oxides and volatile organic compounds; it is not a source of CO itself. Decomposition of sewage releases gases such as methane (CH₄) and hydrogen sulphide (H₂S), not carbon monoxide.

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Iron is extracted from its ore in a blast furnace. The iron that comes directly out of the blast furnace is called pig iron. It contains about 3-4% carbon along with smaller amounts of impurities such as silicon, manganese, phosphorus, and sulphur.

Pig iron is brittle due to its high carbon content and is not suitable for most engineering applications in its raw form. It must be further processed to produce more useful forms of iron and steel:

• Cast iron is produced by remelting pig iron and allowing it to cool in moulds. It still has a relatively high carbon content (2-4%) but has improved properties for casting.
• Wrought iron is nearly pure iron (less than 0.1% carbon) produced by removing most of the carbon and impurities from pig iron. It is soft, malleable, and resistant to corrosion.
• Carbon steel is produced by carefully controlling the carbon content of iron (0.1-1.5%) to achieve specific mechanical properties.

The iron that comes directly from the blast furnace, before any further refining, is pig iron.

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To name this compound using IUPAC nomenclature, first expand the condensed structural formula (CH\(_3\))\(_2\)CHCH(OH)CH\(_2\)C(CH\(_3\))\(_3\):

\[\text{CH}_3-\underset{|}{\overset{\text{CH}_3}{\text{CH}}}-\underset{|}{\overset{\text{OH}}{\text{CH}}}-\text{CH}_2-\underset{|}{\overset{\text{CH}_3}{\underset{|}{\overset{}{\text{C}}}}}(\text{CH}_3)_2\]

Step 1: Find the longest carbon chain containing the OH group.

Tracing through the backbone: CH\(_3\)-CH-CH(OH)-CH\(_2\)-C-CH\(_3\) gives 6 carbons, so the parent chain is hexane.

Step 2: Number to give the OH group the lowest locant.

Numbering from the end nearest the OH group:

• C1: CH\(_3\) (end near the isopropyl group)
• C2: CH (bearing one CH\(_3\) branch)
• C3: CH-OH
• C4: CH\(_2\)
• C5: C (bearing two CH\(_3\) branches)
• C6: CH\(_3\)

OH is on carbon 3. Numbering from the other end would place OH on carbon 4, which is higher, so this direction is correct.

Step 3: Identify substituents.

• Carbon 2: one methyl group
• Carbon 5: two methyl groups

There are three methyl substituents at positions 2, 5, and 5.

Step 4: Construct the name.

The IUPAC name is 2,5,5-trimethylhexan-3-ol.

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The cell notation (also called line notation) for an electrochemical cell follows the convention:

Anode | Anode ion || Cathode ion | Cathode

where the single vertical line (|) represents a phase boundary, and the double vertical line (||) represents the salt bridge separating the two half-cells.

For the reaction Mg + Pb²⁺ → Mg²⁺ + Pb:

• Anode (oxidation): Mg → Mg²⁺ + 2e^-. Magnesium is oxidized, so it is the anode.
• Cathode (reduction): Pb²⁺ + 2e^- → Pb. Lead ions are reduced, so lead is the cathode.

Applying the convention:

Mg | Mg²⁺ || Pb²⁺ | Pb

Using the notation in the options (where I = | and II = ||), this is written as Mg|Mg²⁺||Pb²⁺|Pb.

The anode always appears on the left and the cathode on the right. Within each half-cell, the metal (solid phase) is written adjacent to the outer edge, and the ion (aqueous phase) is written adjacent to the salt bridge.

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Pinking (also called knocking or engine knock) is the premature, uncontrolled auto-ignition of the fuel-air mixture inside an engine cylinder. It produces a metallic rattling noise and can seriously damage the engine over time.

Before petrol is sold, it is evaluated for its octane rating. The octane number measures how resistant the fuel is to pinking. A higher octane number means the petrol is less likely to auto-ignite prematurely and will burn smoothly during the power stroke.

The evaluation of petrol from crude oil before sale is therefore carried out to prevent pinking. Fuels with low octane ratings are either blended with higher-octane components or treated (for example, by adding anti-knock agents) before they are released for sale.

The other options describe petroleum refining processes, not problems to be prevented:

• Reforming is a refinery process that converts low-octane hydrocarbons into higher-octane ones (e.g. converting straight-chain alkanes into cyclic or branched structures).
• Pyrolysis is thermal decomposition of organic materials at high temperatures in the absence of oxygen.
• Cracking is the breaking down of large hydrocarbon molecules into smaller, more useful ones.

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When air is passed through a series of reagents, each one absorbs a specific component:

1. Alkaline pyrogalol (alkaline solution of pyrogallol) absorbs oxygen (O₂). Pyrogallol in alkaline solution reacts readily with oxygen and turns dark brown.
2. Potash (concentrated potassium hydroxide solution, KOH) absorbs carbon dioxide (CO₂). The CO₂ reacts with KOH to form potassium carbonate: CO₂ + 2KOH → K₂CO₃ + H₂O.
3. Fused calcium chloride (CaCl₂) in a U-tube absorbs water vapour (H₂O). Anhydrous CaCl₂ is a powerful desiccant (drying agent).

The main components of air are nitrogen (~78%), oxygen (~21%), argon and other noble gases (~0.9%), carbon dioxide (~0.04%), and water vapour (variable). After removing oxygen, carbon dioxide, and water vapour, the components that remain unabsorbed are noble gases and nitrogen. These are chemically inert (noble gases) or unreactive with the reagents used (nitrogen), so none of the three reagents can remove them.

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The equation Na\(_2\)X \(\rightleftharpoons\) 2Na\(^+\) + X\(^{2-}\) shows the compound Na\(_2\)X dissociating into its constituent ions: sodium ions (Na\(^+\)) and an anion X\(^{2-}\).

This dissociation into oppositely charged ions is the hallmark of an ionic bond. In ionic bonding, one or more electrons are transferred from a metal atom (here, sodium) to a non-metal atom (here, X). Sodium loses one electron to form Na\(^+\), while X gains two electrons to form X\(^{2-}\). Two sodium atoms are needed to supply the two electrons that X requires.

The other bond types do not fit:

• A covalent bond involves the sharing of electron pairs between atoms, not transfer and complete dissociation into ions.
• A dative (coordinate) bond is a special covalent bond where both shared electrons come from one atom.
• A metallic bond involves a "sea" of delocalised electrons shared among metal atoms in a lattice - it does not produce discrete anions like X\(^{2-}\).

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The basicity of an acid is the number of replaceable hydrogen ions (\(\text{H}^+\)) that one molecule of the acid can donate in a reaction with a base.

The compound \(\text{C}_2\text{H}_2\text{O}_4\) is oxalic acid (also called ethanedioic acid). Its structural formula is:

\(\text{HOOC-COOH}\)

Oxalic acid contains two carboxyl groups (\(-\text{COOH}\)). Each carboxyl group carries one hydrogen atom that can be released as \(\text{H}^+\) during a neutralisation reaction. The remaining hydrogen atoms in the molecule are bonded to carbon and are not ionisable.

Since there are two replaceable hydrogen atoms, the basicity of oxalic acid is 2. This means it is a dibasic acid (also called a diprotic acid).

The neutralisation reaction with sodium hydroxide confirms this:

Two moles of NaOH are required to completely neutralise one mole of oxalic acid, confirming a basicity of 2.

When determining basicity, count only the hydrogen atoms bonded to oxygen in carboxyl or hydroxyl groups, not those bonded directly to carbon.

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Carbohydrates follow the general formula \(\text{C}_x(\text{H}_2\text{O})_y\). To find the value of x for fructose, you need to know the molecular formula of fructose.

Fructose has the molecular formula C₆H₁₂O₆. Rewriting this in the carbohydrate general formula:

\[\text{C}_6\text{H}_{12}\text{O}_6 = \text{C}_6(\text{H}_2\text{O})_6\]

Comparing with \(\text{C}_x(\text{H}_2\text{O})_y\), the value of x = 6 (and y = 6 as well).

Fructose is a monosaccharide (simple sugar) that is an isomer of glucose. Both have the same molecular formula C₆H₁₂O₆, but they differ in structural arrangement: glucose is an aldose (contains an aldehyde group) while fructose is a ketose (contains a ketone group).

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Dilute nitric acid (HNO\(_3\)) is an oxidising acid, which means it usually oxidises the metal and is itself reduced to nitrogen oxides (such as NO or NO\(_2\)) rather than producing hydrogen gas. This is different from non-oxidising acids like dilute HCl or dilute H\(_2\)SO\(_4\), which readily liberate H\(_2\) with reactive metals.

However, magnesium (Mg) is an exception. Because magnesium is extremely reactive (high up in the electrochemical series), it reacts so vigorously with very dilute HNO\(_3\) that the reaction proceeds faster than the acid can act as an oxidising agent. The result is that hydrogen gas is liberated:

\[\text{Mg} + 2\text{HNO}_3\text{(very dilute)} \rightarrow \text{Mg(NO}_3\text{)}_2 + \text{H}_2\uparrow\]

Copper (Cu) is below hydrogen in the activity series and cannot displace hydrogen from any acid under normal conditions. Zinc (Zn) reacts with dilute HNO\(_3\) but produces NO gas rather than H\(_2\), because it is not reactive enough to overcome the oxidising nature of the acid. Calcium (Ca) is very reactive but reacts explosively with water itself and, in practice with dilute HNO\(_3\), produces nitrogen oxides or ammonia rather than clean H\(_2\) liberation; the standard examination answer for this question is magnesium.

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The compound CH₃-CH₂-COOCH₂-CH₃ contains the ester functional group (-COO-). To identify the reactants that formed this ester, split the structure at the ester linkage (between the carbonyl carbon and the oxygen bonded to the alkyl group).

The ester bond in -COO- comes from two parts:

• The acid part (to the left of -COO-): CH₃-CH₂-COO-. This corresponds to the carboxylate portion of propanoic acid (CH₃CH₂COOH), a three-carbon carboxylic acid.
• The alcohol part (to the right of -COO-): -CH₂-CH₃. This corresponds to the alkyl group from ethanol (CH₃CH₂OH), a two-carbon alcohol.

The ester is therefore ethyl propanoate, formed from propanoic acid and ethanol:

\[\text{CH}_3\text{CH}_2\text{COOH} + \text{CH}_3\text{CH}_2\text{OH} \rightleftharpoons \text{CH}_3\text{CH}_2\text{COOCH}_2\text{CH}_3 + \text{H}_2\text{O}\]

The correct reactants are propanoic acid and ethanol.

Exam tip: To identify the parent acid and alcohol of an ester, break the molecule at the single-bond oxygen in the -COO- group. The fragment bonded to the carbonyl (C=O) gives the acid; the fragment bonded through the oxygen gives the alcohol.

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Reforming is a petroleum refinery process that rearranges the molecular structure of hydrocarbons to produce higher-octane fuels and aromatic compounds. The most common type is catalytic reforming, which converts naphthenes (cycloalkanes) and straight-chain alkanes into aromatic hydrocarbons such as benzene, toluene, and xylene, typically using a platinum-based catalyst at high temperature.

The conversion of cyclohexane to benzene is a classic example of reforming. In this reaction, cyclohexane (C₆H₁₂) undergoes catalytic dehydrogenation, losing three molecules of hydrogen to form benzene (C₆H₆):

\[ \text{C}_6\text{H}_{12} \xrightarrow{\text{Pt catalyst, heat}} \text{C}_6\text{H}_6 + 3\text{H}_2 \]

This aromatization reaction increases the octane rating of the fuel fraction and produces valuable aromatic feedstocks for the chemical industry.

The other options describe different processes:

• Converting hexene to hexane is hydrogenation (addition of hydrogen across a double bond).
• Converting hexane to carbon(IV) oxide and water vapour is combustion (burning in oxygen).
• Converting hexane to butane and ethane is cracking (breaking larger molecules into smaller ones).

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Fermentation is the biochemical process in which enzymes (particularly zymase, found in yeast) convert glucose into ethanol and carbon dioxide. The overall equation is:

\[\text{C}_6\text{H}_{12}\text{O}_6 \xrightarrow{\text{zymase}} 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2\]

This is an anaerobic process, meaning it occurs without oxygen. The key word in the question is enzymatic, which points directly to fermentation, since it is the only process among the given options that is enzyme-catalysed.

Polymerization is the joining of small monomer molecules into a large polymer chain. Hydrogenation is the addition of hydrogen gas across unsaturated bonds, typically using a metal catalyst such as nickel. Saponification is the alkaline hydrolysis of fats or oils to produce soap and glycerol. None of these processes involves the enzymatic breakdown of glucose to ethanol.

Whenever a question mentions the biological or enzymatic conversion of sugars to alcohol, the answer is fermentation.

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The energy profile diagram shows the energy changes during a chemical reaction. The reactants (A+B) start at an energy level of approximately 30 units, while the products (C+D) end at approximately 50 units. The activation energy peak reaches about 80 units.

Since the products have a higher energy level than the reactants, the reaction has absorbed energy from the surroundings. This net gain in energy by the reacting system is the defining characteristic of an endothermic reaction. The energy difference between products and reactants (\ (\Delta H\)) is positive, confirming that heat was taken in rather than released.

An exothermic reaction would show products at a lower energy level than reactants, indicating a release of energy. Here, the upward shift from reactants to products clearly indicates energy absorption.

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A diagonal relationship in the periodic table refers to the similarity in properties between an element in Period 2 and the element diagonally below and to its right in Period 3. This occurs because moving one period down increases size and metallic character, while moving one group to the right decreases them, so the two effects partially cancel out.

The well-established diagonal pairs are:

• Li (Period 2, Group 1) and Mg (Period 3, Group 2)
• Be (Period 2, Group 2) and Al (Period 3, Group 13)
• B (Period 2, Group 13) and Si (Period 3, Group 14)

From the given options, B and Si is one of the classic diagonal pairs. They share similar properties such as forming covalent compounds, acting as semiconductors, and forming acidic oxides.

The other options are not diagonal pairs:

• Be and Si are two groups apart diagonally, not one.
• Na and Be are in adjacent periods but Na is below and to the left of Be, not diagonal in the correct direction.
• Li and Al are separated by two groups in the diagonal direction.

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The alkynes are a homologous series of unsaturated hydrocarbons containing a carbon-carbon triple bond. Their general formula is:

\[\text{C}_n\text{H}_{2n-2}\]

The series begins at \(n = 2\) (since at least two carbon atoms are needed to form a triple bond):

The 5th member has \(n = 6\): \(\text{C}_6\text{H}_{2(6)-2} = \text{C}_6\text{H}_{10}\).

C₅H₈ is the 4th member, not the 5th. C₅H₁₀ and C₆H₁₂ fit the alkene general formula (C_nH_2n), not the alkyne formula.

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The homologous series of alkenes are unsaturated hydrocarbons that contain exactly one carbon-carbon double bond (C=C). Their general molecular formula is \(\text{C}_n\text{H}_{2n}\), where n is the number of carbon atoms (n >= 2).

To verify, consider a few members:

• Ethene (n = 2): C₂H₄ = C₂H₂₍₂₎
• Propene (n = 3): C₃H₆ = C₃H₂₍₃₎
• Butene (n = 4): C₄H₈ = C₄H₂₍₄₎

Each formula fits \(\text{C}_n\text{H}_{2n}\).

The other general formulae belong to different homologous series: \(\text{C}_n\text{H}_{2n+2}\) represents alkanes (saturated hydrocarbons), \(\text{C}_n\text{H}_{2n-2}\) represents alkynes (with a triple bond), and \(\text{C}_n\text{H}_{2n+1}\text{OH}\) represents alkanols (alcohols).

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Baking powder is a mixture of sodium hydrogen carbonate (baking soda) and a solid acid. The acid is needed because sodium hydrogen carbonate only releases carbon dioxide gas, the substance that makes dough rise, when it reacts with an acid:

\[ \text{NaHCO}_3 + \text{acid} \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{salt} \]

Tartaric acid, \( \text{C}_4\text{H}_6\text{O}_6 \), is a naturally occurring organic acid obtained mainly from grapes, and it is one of the classic solid acids used to formulate baking powder because it is stable when dry but dissolves and reacts quickly once water is added to the dough or batter. The same acid, because it has a pleasant sharp taste and is safe to consume in small amounts, is also added to soft drinks to give them their tart, refreshing flavour and to help balance the sweetness of the sugar in the drink.

The other acids listed do not fit both uses. Fatty acids are found in oils and fats and are not used as leavening or flavouring agents in drinks. Boric acid is toxic in the concentrations relevant to food and is not permitted as a food additive. Citric acid is common in fruit-flavoured drinks but is not the acid traditionally paired with sodium hydrogen carbonate in the classic baking-soda and soft-drink formulation being tested here.

When a question links a food acid to two different uses at once, check that the acid is both chemically suited to the reaction involved (reacting with a base to release gas) and safe and pleasant enough to be consumed directly, since not every food-grade acid satisfies both conditions.

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Freons are a group of chlorofluorocarbons (CFCs) - synthetic compounds containing chlorine, fluorine, and carbon. They were widely used as propellants in aerosol cans, as refrigerants in air conditioners and refrigerators, and as solvents in industrial cleaning.

When released into the atmosphere from these sources, freons rise to the stratosphere where ultraviolet radiation breaks them down, releasing chlorine atoms. These chlorine atoms catalytically destroy ozone molecules, contributing to the depletion of the ozone layer.

Fossil fuel combustion releases carbon dioxide, sulphur dioxide, and nitrogen oxides, but not freons. Photosynthesis is a biological process that produces oxygen and consumes carbon dioxide. Organic decay releases methane and carbon dioxide. None of these processes involve freons.

The Montreal Protocol (1987) restricted the production and use of CFCs, leading to a gradual recovery of the ozone layer.

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A blowing agent is a substance used to produce a cellular structure (foam) in materials such as plastics, rubber, and insulation. The term "blowing" refers specifically to the process of expanding a material by generating gas bubbles within it during manufacture.

Chlorofluorocarbons (CFCs) were widely used as blowing agents in the foam industry because they vaporise at low temperatures, creating uniform gas pockets that give foam products their lightweight, insulating structure. Expanded polystyrene, polyurethane foam, and similar products were traditionally manufactured using CFCs as the blowing agent.

While CFCs also have applications as refrigerants and aerosol propellants, those uses are distinct from the role of a blowing agent. A refrigerant absorbs and releases heat during phase changes in a cooling cycle, and a propellant provides pressure to expel contents from a container. Neither of these functions involves creating foam. The tyre industry does not use CFCs as blowing agents.

The key word in the question is "blowing agent," which points specifically to foam production.

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This is a Faraday's law of electrolysis problem. The relationship between mass deposited, current, and time is:

\[m = \frac{M \times I \times t}{n \times F}\]

where \(m\) = mass deposited (g), \(M\) = molar mass, \(I\) = current (A), \(t\) = time (s), \(n\) = number of electrons transferred per ion, and \(F\) = Faraday constant (96500 C/mol).

For aluminium: \(\text{Al}^{3+} + 3e^- \rightarrow \text{Al}\), so \(n = 3\), \(M = 27\), \(m = 9\) g, \(I = 18\) A.

Rearranging for time:

\[t = \frac{m \times n \times F}{M \times I}\]

\[t = \frac{9 \times 3 \times 96500}{27 \times 18}\]

\[t = \frac{2\,605\,500}{486}\]

\[t = 5360.49 \text{ seconds}\]

Converting to minutes:

\[t = \frac{5360.49}{60} = 89.34 \text{ minutes}\]

The time required is 89.34 minutes.

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According to Graham's law of diffusion, the rate of diffusion of a gas is inversely proportional to the square root of its molar mass:

\[\text{Rate} \propto \frac{1}{\sqrt{M}}\]

This means lighter gases diffuse faster and heavier gases diffuse slower. To arrange gases in order of increasing rate of diffusion, we arrange them from heaviest (slowest) to lightest (fastest).

Calculate the molar masses of the gases that appear in the options:

Arranging from heaviest to lightest (i.e., increasing rate of diffusion):

SO₂ (64) → O₂ (32) → NH₃ (17) → H₂ (2)

This matches the sequence SO₂, O₂, NH₃, H₂. The heaviest gas (SO₂) diffuses most slowly, and the lightest gas (H₂) diffuses most rapidly.

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A reaction is feasible (spontaneous) when the Gibbs free energy change is negative: \(\Delta G < 0\). The relationship between Gibbs free energy, enthalpy, and entropy is:

\[\Delta G = \Delta H - T\Delta S\]

The question states that \(\Delta G^\circ\) is negative. To determine which combination of \(\Delta H\) and \(\Delta S\) guarantees this, consider each option:

• If \(\Delta H\) is positive and \(\Delta S\) is positive: \(\Delta G = (+) - T(+)\). This is negative only at sufficiently high temperatures, so feasibility is not guaranteed at all temperatures.
• If \(\Delta H = 0\) and \(\Delta S\) is positive: \(\Delta G = 0 - T(+) = -T\Delta S\), which is always negative at any temperature above 0 K. This guarantees a negative \(\Delta G\).
• If \(\Delta H\) is positive and \(\Delta S\) is negative: \(\Delta G = (+) - T(-) = (+) + T|\Delta S|\), which is always positive. The reaction would never be feasible.
• If \(\Delta S = 0\): \(\Delta G = \Delta H\), and feasibility depends entirely on the sign of \(\Delta H\), which is not specified.

The only option that ensures \(\Delta G\) is negative under all conditions is \(\Delta H = 0\) and \(\Delta S\) is positive, because the \(-T\Delta S\) term is always negative when \(\Delta S > 0\).

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Anti-freeze is a substance added to the water in a vehicle's radiator to lower its freezing point, preventing the coolant from solidifying in cold weather and potentially cracking the engine block.

Among the options given, propanetriol (glycerol or propane-1,2,3-triol, HOCH\(_2\)CH(OH)CH\(_2\)OH) has historically been used as an anti-freeze. Glycerol is highly soluble in water in all proportions, and when dissolved, it significantly depresses the freezing point of the mixture. This is a colligative property: the dissolved solute particles disrupt the formation of ice crystals, requiring a lower temperature to freeze.

The other options are unsuitable:

• Propanol (CH\(_3\)CH\(_2\)CH\(_2\)OH) is a flammable alcohol not used in radiator systems.
• Propanone (acetone, CH\(_3\)COCH\(_3\)) is a volatile ketone and a solvent, not an anti-freeze.
• Propanal (CH\(_3\)CH\(_2\)CHO) is an aldehyde with no anti-freeze application.

In modern practice, ethylene glycol (ethane-1,2-diol) is more commonly used, but among the four choices provided, propanetriol is the correct answer.

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The structure shown is R-C(=O)-NH-H, which contains a carbonyl group (C=O) directly bonded to a nitrogen atom bearing hydrogen atoms. This is the defining arrangement of the amide functional group (-CONH₂).

An alkanamide (also called an amide) has the general formula R-CONH₂, where R is an alkyl group. The key feature distinguishing it from the other options is the simultaneous presence of both the C=O and the N-H bonds on the same carbon.

An alkylamine (R-NH₂) has nitrogen bonded to an alkyl group but no carbonyl. An alkanone (R-CO-R') has a carbonyl flanked by two carbon groups with no nitrogen. An amino acid would require both an amine group (-NH₂) and a carboxyl group (-COOH) on the same molecule, which is not the case here.

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The fountain experiment demonstrates the very high solubility of certain gases in water. A round-bottom flask is filled with the gas and inverted over a trough of water (often containing an indicator). When a small amount of water enters the flask and dissolves the gas, the pressure inside drops dramatically. Atmospheric pressure then forces water up into the flask in a spectacular fountain.

For this experiment to work, the gas must be extremely soluble in water so that it dissolves almost instantly on contact, creating a near-vacuum inside the flask.

Hydrogen chloride (HCl) is the classic gas used. It is one of the most soluble gases in water: about 450 volumes of HCl dissolve in one volume of water at room temperature, forming hydrochloric acid. Ammonia (NH₃) is also commonly used for the same experiment, but it is not among the given options.

Hydrogen sulphide (H₂S) is only moderately soluble and is extremely toxic, making it unsuitable. Dinitrogen(I) oxide (N₂O, nitrous oxide) and nitrogen(II) oxide (NO, nitric oxide) are both poorly soluble in water and would not produce the dramatic pressure drop needed for the fountain effect.

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In the nitrogen cycle, when organisms die, their proteins and other nitrogenous compounds are broken down by decomposing bacteria in a process called ammonification (or decay). The first product of this decomposition is ammonia (NH₃).

The process occurs in stages:

1. Proteins in dead material are broken down into amino acids by proteolytic enzymes from decomposing bacteria and fungi.
2. The amino acids are further deaminated (the amino group -NH₂ is removed), releasing ammonia (NH₃).

After ammonia is produced, nitrifying bacteria can convert it further: first to nitrites (dioxonitrate(III), NO₂^-) by Nitrosomonas, then to nitrates (trioxonitrate(V), NO₃^-) by Nitrobacter. However, the question asks specifically about the first conversion product of nitrogenous compounds in dead materials, which is ammonia.

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Reduction is the gain of electrons (or a decrease in oxidation state). To identify which species is reduced, track the oxidation states of each element.

In the reaction \(2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}\):

• Sodium (Na): Oxidation state changes from 0 (in elemental Na) to +1 (in NaCl). This is an increase in oxidation state, meaning sodium is oxidised (it loses one electron per atom).
• Chlorine (Cl₂): Oxidation state changes from 0 (in elemental Cl₂) to -1 (in NaCl as Cl^-). This is a decrease in oxidation state, meaning chlorine is reduced (each Cl atom gains one electron).

The species that undergoes reduction is Cl₂, because it is the substance that accepts electrons and has its oxidation state lowered from 0 to -1.

Note that Cl^- is the product of the reduction, not the species that undergoes it. The question asks for the species that undergoes reduction, which is the reactant Cl₂.

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The equation shows propane (\(C_3H_8\)) reacting with chlorine gas (\(Cl_2\)) in the presence of ultraviolet light to produce chloropropane (\(C_3H_7Cl\)) and hydrogen chloride (\(HCl\)).

In this reaction, a hydrogen atom on the propane molecule is replaced by a chlorine atom. This is the hallmark of a substitution reaction, specifically a free-radical substitution. The UV light provides the energy needed to break the \(Cl-Cl\) bond homolytically, generating chlorine free radicals that then attack the alkane.

It is not neutralization (no acid-base reaction), not polymerization (no repeating monomer units are joined), and not oxidation in the classical sense used here. The defining feature is the direct replacement of one atom (H) by another (Cl) in the organic molecule.