Explanation:
(b)Iodine vapours are violet
\(\therefore\) the salt must contain \({I^ - }\)as
\(KI + {H_2}S{O_4} \to KHS{O_4} + HI\)
\(2HI + {H_2}S{O_4}\,\,\,\, \to \mathop {{I_2} + 2{H_2}O + S{O_2}}\limits_{{\rm{violet vapour}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \)