WAEC Chemistry 2011 Paper

Concept:Chlorine, bromine and iodine are halogens in Group 7 and show similar chemical properties, including their reaction with alkalis.Explanation:Halogens undergo disproportionation reactions with alkalis.For example, chlorine reacts with cold dilute sodium hydroxide to form sodium chloride and sodium hypochlorite:$$\mathrm{Cl}_2 + 2\mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{NaOCl} + \mathrm{H}_2\mathrm{O}$$Bromine and iodine react similarly with alkalis, so option D is correct.Option A is false because at room temperature, chlorine is a gas, bromine is a liquid, and iodine is a solid.Option B is false because silver halide precipitates are not all white: $\mathrm{AgCl}$ is white, $\mathrm{AgBr}$ is pale yellow, and $\mathrm{AgI}$ is yellow.Option C is false because reactivity with hydrogen decreases down the group, so iodine does not react violently with hydrogen.Answer:D. react with alkali