JAMB UTME - Chemistry - 2016
Question 1 Report
Which of the following statements is correct about the periodic table?
Answer Details
Question 2 Report
The compound produced when sodium peroxide is heated with excess sodium is
Answer Details
When sodium peroxide (Na2O2) is heated with excess sodium (Na) at high temperature, the resulting compound is sodium oxide (Na2O). This reaction can be represented by the following equation: 2Na2O2 + 4Na → 4Na2O In this reaction, the excess sodium (Na) reacts with the sodium peroxide (Na2O2) to form sodium oxide (Na2O) and release oxygen gas (O2). The reaction is exothermic and produces a large amount of heat. Sodium oxide (Na2O) is a white crystalline solid that is highly reactive with water, forming sodium hydroxide (NaOH) and releasing a large amount of heat. Therefore, it should be handled with care and stored in a dry environment to avoid contact with moisture. In summary, heating sodium peroxide (Na2O2) with excess sodium (Na) produces sodium oxide (Na2O).
Question 3 Report
Which of the following compounds is used as a gaseous fuel?
Question 4 Report
In the laboratory preparation of chlorine from concentrated hydrochloric acid in the presence of potassuim tetraoxomanganate(VII) the produced is dried by passing it through
Answer Details
Question 5 Report
The relative atomic mass of a naturally occurring lithium consisting of 90%73 Li and 10%63 Li is
Answer Details
(90100 x 7) + (10100 x 6)
= 6.3 + 0.6 = 6.9
Question 6 Report
In the extraction of iron, the waste gas from the furnace is a mixture of
Question 7 Report
What is the concentration of a solution containing 2g of NaOH in 100cm3 of solution?
[Na = 23, O = 16, H = 1]
Answer Details
To calculate the concentration of a solution, we need to know the number of moles of the solute (in this case, NaOH) dissolved in a given volume of solution. To do this, we first need to calculate the number of moles of NaOH present in 2g of the compound. The molar mass of NaOH can be calculated as follows: NaOH = 23 + 16 + 1 = 40 g/mol This means that one mole of NaOH weighs 40g. To calculate the number of moles of NaOH in 2g, we can use the following formula: number of moles = mass ÷ molar mass So, the number of moles of NaOH in 2g can be calculated as follows: number of moles = 2 ÷ 40 = 0.05 moles Now that we know the number of moles of NaOH in the solution, we can calculate its concentration. Concentration is usually measured in units of mol/dm3 (moles per cubic decimeter). In this case, we have 100cm3 of solution, which is equivalent to 0.1dm3. So, we can use the following formula to calculate the concentration: concentration = number of moles ÷ volume of solution Substituting the values we have, we get: concentration = 0.05 moles ÷ 0.1 dm3 concentration = 0.50 mol dm-3 Therefore, the concentration of the solution containing 2g of NaOH in 100cm3 of solution is 0.50 mol dm-3. In summary, the concentration of the solution can be calculated by first determining the number of moles of the solute in the solution, and then dividing it by the volume of the solution. For the given solution, the number of moles of NaOH in 2g is 0.05 moles, and the concentration is 0.50 mol dm-3 when dissolved in 100cm3 of solution. Therefore, the correct option is B: 0.50 mol dm-3.
Question 8 Report
In a neutralization reaction involving HCI and NaOH using litmus as indicator, the colour at the end point is
Question 9 Report
MnO-4(aq) + Y + 5Fe2+(aq) → Mn2+(aq) + 5Fe2+(aq) + 4H2O(l)
In the equation above, Y is
Answer Details
Question 10 Report
The radioisotope used in industrial radiography for the rapid checking of faults in welds and casting is
Answer Details
The radioisotope used in industrial radiography for the rapid checking of faults in welds and casting is cobalt-60 (Co-60). Cobalt-60 is a gamma-emitting isotope that produces a very penetrating form of radiation, which makes it ideal for industrial radiography. In this process, the cobalt-60 source is placed on one side of the object being examined, and a special film is placed on the other side. The gamma rays penetrate the object and are absorbed by the film, creating an image that reveals any faults or defects in the material. It is important to note that other radioisotopes such as carbon-14 (C-14), phosphorus-32 (P-32), and iodine-131 (I-131) are not commonly used in industrial radiography due to their lower penetrative power and shorter half-life.
Question 11 Report
n monosaccharide P⇌Q polysaccharide -n water.
In the process above, P and Q respectively represent
Answer Details
Question 12 Report
Which of the following properties is NOT peculiar to matter?
Answer Details
The property that is NOT peculiar to matter is "random motion of particles increases from gas to solid." In general, matter is characterized by its kinetic energy, which refers to the energy that particles possess due to their motion. As matter changes its state, the kinetic energy of its particles also changes, which results in different properties. For example, when matter changes from a solid to a gas, the kinetic energy of its particles increases, and they move more quickly and randomly. Similarly, as matter changes from a liquid to a gas, the random motion of its particles also increases. However, the opposite is true when matter changes from a gas to a solid. As matter loses energy and cools, the random motion of its particles decreases, and they become more ordered and arranged in a crystalline structure. Therefore, the property that is NOT peculiar to matter is that the random motion of particles increases from gas to solid.
Question 13 Report
Cast iron is used in making
Answer Details
Cast iron is a type of iron that is used in making stoves and cookers, as listed in one of the options. Cast iron is a material that is known for its durability and heat retention properties, making it an excellent choice for use in these types of applications. Cast iron is made by melting iron and adding small amounts of carbon and other alloying elements to the mix. The molten metal is then poured into molds, which are typically made of sand, and allowed to cool and solidify. This process creates a material that is strong, durable, and resistant to heat. In the case of stoves and cookers, cast iron is often used because of its ability to absorb and retain heat. This means that once the stove or cooker is heated up, it will stay hot for a long period of time, making it ideal for cooking or baking. Cast iron is also commonly used in the manufacturing of other products, such as chains and agricultural implements, due to its strength and durability. It is not typically used in the production of iron sheets and retort stands, as listed in one of the options, as these items are generally made from other types of metal or materials. In summary, cast iron is a type of iron that is commonly used in the manufacturing of stoves, cookers, chains, and agricultural implements due to its strength, durability, and heat retention properties. It is not typically used in the production of iron sheets, retort stands, nails, or iron rods.
Question 14 Report
The colour of litmus in an alkaline medium is
Answer Details
Litmus is a natural dye that can be extracted from certain lichens. It is commonly used as an indicator to determine whether a substance is acidic or alkaline. Litmus paper is a small strip of paper that is coated with litmus dye and is used to test the pH of a solution. When litmus paper is dipped into an alkaline solution, it turns blue. This is because in an alkaline solution, the concentration of hydroxide ions (OH-) is higher than the concentration of hydrogen ions (H+). The litmus dye reacts with the hydroxide ions in the alkaline solution, causing the paper to turn blue. On the other hand, when litmus paper is dipped into an acidic solution, it turns red. This is because in an acidic solution, the concentration of hydrogen ions (H+) is higher than the concentration of hydroxide ions (OH-). The litmus dye reacts with the hydrogen ions in the acidic solution, causing the paper to turn red. Therefore, the colour of litmus in an alkaline medium is blue, while the colour of litmus in an acidic medium is red.
Question 15 Report
The functional groups present in the compound above are
Question 16 Report
Alkanols have the general molecular formula
Answer Details
Alkanols have the general molecular formula CnH2n+1OH, where n is the number of carbon atoms in the molecule. An alkanol is an organic compound that contains a hydroxyl group (-OH) attached to an alkane, which is a hydrocarbon chain composed of only carbon and hydrogen atoms. It is important to note that the molecular formula for an alkanol will vary depending on the number of carbon atoms in the molecule. For example, methanol (CH3OH) has one carbon atom, while ethanol (C2H5OH) has two carbon atoms, and so on.
Question 17 Report
The metal whose ore can be concentrated by passing it through a magnetic separator is
Answer Details
Question 18 Report
N2O4(aq) ⇌ 2NO2(g) △ H = +ve
In the reaction above, an increase in temperature will
Answer Details
The given chemical equation represents the equilibrium reaction between N2O4 (aq) and 2NO2 (g) with the release of heat (H=+ve). When the temperature of the reaction mixture is increased, the system will try to counteract the stress by shifting the equilibrium position in a direction that will partially alleviate the stress. According to Le Chatelier's principle, an increase in temperature favors an endothermic reaction, which means that the equilibrium position will shift towards the direction that absorbs heat. In this case, the forward reaction (N2O4 → 2NO2) is endothermic, meaning that it absorbs heat. Therefore, an increase in temperature will shift the equilibrium position to the right, favoring the formation of more NO2 (g) from N2O4 (aq). As a result, the concentration of NO2 (g) will increase, while the concentration of N2O4 (aq) will decrease. So, the correct answer to the question is that an increase in temperature will increase the production of the product NO2 (g) by shifting the equilibrium position to the right. It will not affect the equilibrium constant (Kc), which is a constant at a given temperature and does not change with the changes in concentration or reaction conditions.
Question 19 Report
The curve depicts titration between
Question 20 Report
Ammonium chloride can be separated from its mixture with common salt by
Answer Details
Ammonium chloride can be separated from its mixture with common salt by sublimation. Sublimation is a process in which a solid changes directly into a gas without passing through the liquid state. Ammonium chloride has a higher vapor pressure than common salt, which means that it can be converted into a gas more easily than common salt. When ammonium chloride is heated, it sublimes, or changes directly from a solid to a gas, leaving behind the common salt. To separate ammonium chloride from its mixture with common salt, the mixture is heated. The ammonium chloride sublimes and is collected as a gas, while the common salt remains behind as a solid. The ammonium chloride gas can be collected and condensed back into a solid form by cooling. This process is used to purify ammonium chloride and is also used in the laboratory to separate mixtures of solids that can be sublimed. In summary, ammonium chloride can be separated from its mixture with common salt by sublimation, which involves heating the mixture to convert the ammonium chloride directly from a solid to a gas, leaving behind the common salt.
Question 21 Report
The industrial preparation of hydrogen gas from water gas is referred to as
Answer Details
The industrial preparation of hydrogen gas from water gas is referred to as the Bosch process. The Bosch process involves passing a mixture of steam and carbon monoxide over a hot iron catalyst, which causes the carbon monoxide to react with the steam to form hydrogen gas. This process is highly efficient and is widely used in the production of hydrogen gas for various industrial and energy applications. It is important to note that the Bosch process should not be confused with other processes such as the Haber process (used for the production of ammonia), the Bayer process (used for the production of aluminum), or the Contact process (used for the production of sulfuric acid).
Question 22 Report
The principle of column chromatography is based on th ability of the constituents to
Answer Details
Column chromatography is a separation technique used in chemistry to separate and purify individual components of a mixture. The principle of column chromatography is based on the ability of the constituents of a mixture to move at different speeds in the column. The column used in chromatography is usually filled with a stationary phase, which is a material that does not move, such as silica gel or alumina. The mixture to be separated is added to the top of the column, and a solvent is added to the column and allowed to flow through the stationary phase by gravity or by applying pressure. The individual components of the mixture will interact differently with the stationary phase and the solvent, resulting in different rates of movement through the column. Some components will move more slowly, while others will move more quickly. This difference in movement rate will cause the components to become separated as they move through the column. The individual components can then be collected as they exit the column at different times. The separation is based on a combination of factors, including the polarity and size of the molecules, as well as the type of stationary phase and solvent used. Therefore, the correct answer to the question is: Move at different speeds in the column.
Question 23 Report
CH4(g) + CI2(g) ? CH2CI(s) + HCIg
The major factor that influences the rate of the reaction above is
Question 24 Report
The process that requires the use of hardwater in its operation is
Question 26 Report
An example of an acidic oxide is
Answer Details
An acidic oxide is a type of oxide that reacts with water to form an acid. In other words, an acidic oxide has the ability to donate hydrogen ions (protons) to form an acid. One example of an acidic oxide is sulfur dioxide (SO2). When sulfur dioxide reacts with water, it forms sulfuric acid (H2SO4), which is a strong and highly corrosive acid. SO2 + H2O → H2SO4 So, the correct answer is SO2.
Question 27 Report
In an electrochemical cell, polarization is caused by
Answer Details
In an electrochemical cell, polarization is caused by the accumulation of hydrogen gas on the surface of the cathode. An electrochemical cell converts chemical energy into electrical energy through the flow of electrons between two electrodes, the anode (negative electrode) and the cathode (positive electrode), connected by an external circuit. During the operation of the cell, a potential difference is created between the anode and cathode, driving the flow of electrons from the anode to the cathode, which results in the production of electricity. However, during the operation of the cell, the accumulation of hydrogen gas on the surface of the cathode can cause polarization, which is the reduction in the rate of the electrochemical reaction. This is because the hydrogen gas layer acts as a barrier that prevents the electrolyte from coming into contact with the cathode, which reduces the rate of the reaction. As a result, the potential difference between the anode and cathode decreases, which reduces the efficiency of the cell. Therefore, in an electrochemical cell, polarization is caused by the accumulation of hydrogen gas on the surface of the cathode. This can be minimized by using a catalyst or by periodically removing the hydrogen gas layer to restore the rate of the electrochemical reaction.
Question 28 Report
The number of electronic shells contained in an atom with electron configuration 1s22s22p63s23p64s2 is
Answer Details
Question 29 Report
An isotope has an atomic number of 15 and a mass number of 31. The number of protons it contains is
Answer Details
The atomic number of an element is the number of protons it has in its nucleus. The atomic number of the isotope is given as 15, which means it contains 15 protons. The mass number of the isotope is given as 31, which is the sum of the number of protons and neutrons in the nucleus. Since the mass number is 31 and the atomic number is 15, the number of neutrons can be found by subtracting the atomic number from the mass number: number of neutrons = mass number - atomic number number of neutrons = 31 - 15 number of neutrons = 16 Therefore, the isotope has 15 protons, which is the same as its atomic number. Answer option (B) is correct.
Question 30 Report
Ethanol is soluble in water due to the presence of a
Answer Details
Ethanol is soluble in water due to the presence of a hydroxyl group (-OH). The hydroxyl group allows ethanol to form hydrogen bonds with water molecules, which results in the molecule's solubility in water. A carbonyl group (-C=O) would make a molecule less soluble in water, as the carbonyl group is a polar functional group that would interact less favorably with water molecules. A phenyl group (-C6H5) is a hydrophobic group that would also make a molecule less soluble in water. A methyl group (-CH3) is also a hydrophobic group that would make a molecule less soluble in water.
Question 32 Report
The arrangement of particles in crystal lattices can be studied using
Answer Details
The arrangement of particles in crystal lattices can be studied using X-rays. X-rays are a type of electromagnetic radiation that can penetrate solids and are commonly used in medical imaging and other applications. When X-rays are directed at a crystal lattice, they are diffracted, or bent, by the atoms in the lattice. The pattern of diffraction depends on the arrangement of atoms in the crystal lattice. By analyzing the pattern of diffraction, scientists can determine the arrangement of atoms in the crystal lattice and other properties of the crystal, such as its symmetry and unit cell dimensions. This technique, known as X-ray crystallography, has been used to determine the structures of many important molecules, including DNA, proteins, and drugs. It is a powerful tool for studying the structure and function of biological molecules and materials science. In summary, X-rays can be used to study the arrangement of particles in crystal lattices through a technique called X-ray crystallography. The diffraction pattern produced by the X-rays reveals information about the arrangement of atoms in the crystal lattice.
Question 34 Report
The ability of carbon to form long chains is referred to as
Answer Details
The ability of carbon to form long chains is referred to as catenation. Catenation is the ability of an element to form long chains or rings with atoms of the same element. Carbon has a unique ability to catenate, which means it can form long chains, branched chains, and rings of carbon atoms. This ability is due to the unique electron configuration of carbon atoms. Carbon has four valence electrons, which allows it to form four covalent bonds with other atoms. Because of this, carbon can form strong and stable bonds with other carbon atoms, allowing it to form long chains and rings. This property of catenation is essential to the formation of organic compounds, which are compounds that contain carbon. Organic compounds are found in living organisms, and they form the basis of life on Earth. The ability of carbon to catenate is also responsible for the diverse range of organic compounds that exist, from simple hydrocarbons like methane to complex molecules like proteins and DNA. In summary, catenation is the ability of an element to form long chains or rings with atoms of the same element. Carbon has a unique ability to catenate, which allows it to form long chains, branched chains, and rings of carbon atoms. This ability is essential to the formation of organic compounds, which form the basis of life on Earth.
Question 35 Report
The condition required for corrosion to take place is the presence of
Answer Details
The presence of water and oxygen is required for corrosion to take place. When a metal is exposed to oxygen and water, a chemical reaction occurs that forms metal oxide or hydroxide, which weakens and breaks down the metal. Carbon (IV) oxide may also contribute to corrosion, but it is not a necessary component. Therefore, "Water and Oxygen" is the correct answer.
Question 36 Report
The pollutant that contributes to the depletion of the ozone layer is
Answer Details
The pollutant that contributes to the depletion of the ozone layer is CFCs, which stands for Chlorofluorocarbons. CFCs are a class of chemical compounds that contain chlorine, fluorine, and carbon atoms. They were widely used in aerosol sprays, refrigerants, and other industrial applications because they are stable, non-toxic, and nonflammable. However, CFCs are also very stable in the atmosphere and can remain there for many years without being broken down. When CFCs are released into the atmosphere, they eventually reach the stratosphere, where they are broken down by ultraviolet radiation from the sun. This process releases chlorine atoms, which then react with ozone molecules, breaking them apart and depleting the ozone layer. The ozone layer is important because it protects life on Earth from harmful UV radiation from the sun. The depletion of the ozone layer leads to increased UV radiation reaching the Earth's surface, which can cause skin cancer, cataracts, and other health problems in humans, as well as damage to crops and marine organisms. NO2, SO2, and CO are not ozone-depleting pollutants. NO2 (nitrogen dioxide) is a common air pollutant that can cause respiratory problems and acid rain. SO2 (sulfur dioxide) is another air pollutant that is produced by burning fossil fuels and can cause respiratory problems and acid rain. CO (carbon monoxide) is a colorless, odorless gas that is produced by incomplete combustion and can be deadly in high concentrations.
Question 38 Report
A chemical reaction which the hydration energy is greater than the lattice energy is referred to as
Answer Details
A chemical reaction involves the breaking and formation of chemical bonds between atoms or molecules. The energy required to break bonds is known as bond energy, and the energy released when new bonds form is known as bond formation energy. The energy change of a reaction can be affected by several factors, including the hydration energy and lattice energy of the reactants. The hydration energy is the energy released when a substance dissolves in water. The lattice energy is the energy required to break the ionic bonds in a solid. When the hydration energy is greater than the lattice energy, it means that more energy is released when the substance dissolves in water than is required to break the ionic bonds in the solid. This type of reaction is referred to as an exothermic reaction, because it releases energy in the form of heat. In other words, the system loses energy and the surroundings gain energy. Examples of exothermic reactions include combustion reactions and many types of acid-base reactions. Therefore, the correct answer to the question is: an exothermic reaction.
Question 40 Report
What volume of 0.5 mol dm-3 H2SO4 will exactly neutralize 20cm3 of 0.1 mol dm-3 NaOH solution?
Answer Details
To solve this problem, we can use the concept of mole ratios and the equation: H2SO4 + 2NaOH -> Na2SO4 + 2H2O From the equation, we can see that 1 mole of H2SO4 reacts with 2 moles of NaOH. Therefore, to neutralize 1 mole of NaOH, we need 1/2 mole of H2SO4. This means that for the given 0.1 mol dm-3 NaOH solution, we need 0.05 moles of H2SO4 to neutralize it. Now, we can use the equation: moles = concentration x volume (in dm3) to calculate the volume of 0.5 mol dm-3 H2SO4 needed to neutralize 0.05 moles of NaOH. 0.5 x V = 0.05 V = 0.05 / 0.5 V = 0.1 dm3 But the volume of NaOH solution given in the problem is 20 cm3 or 0.02 dm3. Therefore, the volume of H2SO4 required to neutralize it is: V = 0.1 dm3 x (0.02 dm3 / 1 dm3) V = 0.002 dm3 or 2 cm3 Therefore, the answer is option A, 2.0 cm3.
Question 41 Report
The gas that is used for the treatment of cancer is
Answer Details
The gas that is used for the treatment of cancer is not listed in the options provided. However, a gas commonly used in cancer treatment is a form of radioactive gas called Radon. Radon gas is a byproduct of the decay of radioactive elements such as uranium and radium, and can be found naturally in soil and rock. In cancer treatment, a highly purified form of radon gas is used to deliver targeted doses of radiation to cancerous cells in the body. This is known as radon therapy. Radon therapy works by injecting small amounts of radon gas into the body, usually in the form of a gas or liquid. The radon gas then emits alpha particles, which are highly energetic particles that can penetrate the body and destroy cancerous cells. The targeted nature of the radiation means that healthy cells surrounding the cancerous cells are not as affected. Although radon therapy can be an effective form of cancer treatment, it is important to note that the use of radon gas is highly regulated and controlled due to the risks associated with exposure to radiation. Radon gas is typically only used in very specific circumstances and under the supervision of highly trained medical professionals. In summary, the gas that is used for the treatment of cancer is not neon, xenon or argon, but rather a form of radioactive gas called radon. Radon therapy involves delivering targeted doses of radiation to cancerous cells using highly purified radon gas, which emits alpha particles to destroy the cancerous cells. However, it's important to note that the use of radon gas in cancer treatment is highly regulated and controlled due to the risks associated with exposure to radiation.
Question 42 Report
Which of the following is not an alkali?
Answer Details
NH3 (Ammonia) is not an alkali. Alkalis are typically defined as bases that are soluble in water and have a pH greater than 7. They are often composed of metal hydroxides, such as NaOH (Sodium Hydroxide) and Ca(OH)2 (Calcium Hydroxide). Ammonia, on the other hand, is a compound made of nitrogen and hydrogen and is a weak base. It does not have the properties of an alkali as it does not have a pH greater than 7 and is not soluble in water.
Question 43 Report
The compound above exhibits
Question 44 Report
The compounds CH3CH2CHO and CH3COCH3 can be distinguished from each other using
Question 45 Report
Which of the following statements is true about 2-methylpropane and butane
Question 46 Report
An example of a solid emulsion is
Answer Details
An example of a solid emulsion is butter. Emulsion is a type of mixture in which two or more immiscible liquids are dispersed in each other. In an emulsion, one liquid is dispersed as small droplets throughout the other liquid. The droplets are stabilized by a substance called an emulsifier, which helps to prevent them from coalescing and separating. In the case of butter, it is a solid emulsion of water droplets dispersed in a continuous fat phase. The emulsifier in butter is a combination of proteins and phospholipids. These emulsifiers help to stabilize the water droplets in the fat phase, preventing them from coalescing and separating. Butter is made by churning cream, which is a mixture of milk fat and water. During churning, the fat globules in the cream collide and aggregate, forming solid clumps. These clumps are then kneaded together to form a solid mass, which is butter. The water droplets, which are also present in the cream, become dispersed throughout the butter in the form of small droplets. In summary, an example of a solid emulsion is butter, which is a mixture of water droplets dispersed in a continuous fat phase. The emulsifier in butter helps to stabilize the water droplets and prevent them from coalescing and separating.
Question 48 Report
Calculate the volume in cm3 of oxygen evolved as s.t.p. when a current of 5 A is passed through acidified water for 193s
{F = 96500 Cmol-1, Molar volume of a gas at s.t.p. = 22.4 dm3}
Answer Details
According to Faraday's laws of electrolysis, the mass of a substance produced at an electrode during electrolysis is directly proportional to the amount of electric charge passed through the cell. The relationship can be expressed as: mass of substance produced = (electric charge passed x molar mass of substance) / (Faraday's constant x charge on one electron) We can rearrange this equation to find the volume of gas produced at STP, as follows: volume of gas produced at STP = (electric charge passed x molar volume of gas at STP) / (Faraday's constant x charge on one electron) Substituting the given values into the equation, we get: volume of gas produced at STP = (5 A x 193 s x 22.4 dm3) / (96500 Cmol-1 x 1.602 x 10-19 C) Simplifying this expression, we get: volume of gas produced at STP = 0.056 dm3 Therefore, the volume of oxygen evolved as STP when a current of 5 A is passed through acidified water for 193 s is 0.056 dm3, or 56.000 cm3. The correct answer is.
Question 49 Report
The product formed when propanol is heated over a copper catalyst in the absence of oxygen are
Answer Details
Question 50 Report
The enzyme used in the hydrolysis of starch to dextrin and maltose is
Answer Details
The enzyme used in the hydrolysis of starch to dextrin and maltose is amylase. Amylase is an enzyme that breaks down carbohydrates such as starch and glycogen into smaller sugars such as glucose and maltose. In the human body, amylase is found primarily in the pancreas and saliva, and is responsible for the initial breakdown of starch into maltose during the process of digestion. Therefore, option C (Amylase) is the correct answer.
