Answer: B. The reaction is Cl₂ + 2KI → 2KCl + I₂; the brown solution is iodine. Track the oxidation states: chlorine goes from 0 to −1, so its oxidation state decreases — chlorine is reduced (it gains electrons).
Iodide ions go from −1 to 0 in iodine, so they lose electrons and are oxidised. Option A is wrong because reduction is the gain of electrons, not loss. Option C is wrong because iodide ions lose electrons. Option D is wrong because chlorine is more reactive and more electronegative than iodine, so chlorine attracts electrons more strongly.
The correct statement is simply that the oxidation state of chlorine decreases.
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