$\frac{\mathrm{K}.\mathrm{I}. (\mathrm{aq}.) + \text{'}\mathrm{A}\text{'} \left(\mathrm{reagent}\right)}{\downarrow }$

$\underset{\downarrow }{ [\mathrm{Brown} \mathrm{solution} \mathrm{of} \text{'}\mathrm{B}\text{'}]}$

     $[\mathrm{White} \mathrm{ppt}. \mathrm{of} \text{'}\mathrm{C}\text{'}]$

Compound 'A" and 'C' may be:

When copper sulphate  ${\mathrm{CuSO}}_4$  is treated with potassium iodide (KI), it precipitates cuprous iodide  $($${\mathrm{Cu}}_2{\mathrm{I}}_2$$)$  liberates iodine gas ${\mathrm{I}}_2$ and produces potassium sulphate ${\mathrm{K}}_2{\mathrm{SO}}_4$

$\text{ (K.I. (aq.) }+{\mathrm{CuSO}}_4$(reagent)$\to$Brown solution of $\text{'}{B}^{\text{'}}+{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3\to {\mathrm{Cu}}_2{\mathrm{I}}_2$