A solution of a salt in concentrated sulphuric acid produced a deep blue colour with starch iodide solution. The salt may be :

The reaction takes place in the following way,

${\mathrm{Br}}^{-}\stackrel{\text{ conc. }{\mathrm{H}}_2{\mathrm{SO}}_4}{⟶}{\mathrm{Br}}_2\stackrel{\mathrm{KI}}{⟶}{\mathrm{I}}_2$     

(it turns starch iodide solution deep blue). The salt is bromide.