(a) Arrange the first three members of the halogen family in their increasing order of electronegativity. Give the reason for your answer. (b) State and exp...

Answer Details

(a) Increasing order of electronegativity of the first three halogens

The first three members of the halogen family are fluorine, chlorine and bromine. In increasing order of electronegativity:

Reason: Electronegativity is the tendency of an atom to attract the shared (bonding) pair of electrons towards itself. Down the group the atomic size (number of shells) increases, so the bonding electrons are farther from the nucleus and are more shielded from it. The effective nuclear attraction for the shared electrons therefore decreases down the group. Since fluorine is the smallest atom its nucleus attracts electrons most strongly, while bromine, being the largest of the three, attracts them least. Hence electronegativity increases from bromine to chlorine to fluorine.

(b) Reaction of chlorine with starch-iodide paper

Observation: the starch-iodide paper turns blue-black.

Explanation: Chlorine is a stronger oxidizing agent (more electronegative) than iodine, so it displaces/oxidizes the iodide ions in the paper to liberate free iodine:

The liberated iodine then reacts with the starch present in the paper to form the characteristic blue-black starch-iodine complex, confirming the presence of chlorine.