Which of the following salt would give SO _ 2 with hot and dil H _...

When ${Na}_{2}{SO}_{3}$ reacts with hot and dil ${H}_{2}{SO}_{4},$ it gives ${SO}_{2} \left(g\right)$ which decolourises bromine-water.

The reaction proceed as follows:

(i) ${Na}_{2}{SO}_{3} + {H}_{2}{SO}_{4} ⟶ {Na}_{2}{SO}_{4} + {SO}_{2} + {H}_{2}O$

(ii) ${Br}_{2} + {H}_{2}O ⟶ 2HBr + \left[O\right]$

(iii) ${SO}_{2} + \left[O\right] ⟶ {SO}_{3}$& (decolourisation of bromine-water)