${ }^{\text{'}}\mathrm{X}+{\mathrm{CuSO}}_4⟶\underset{\downarrow {\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3}{{\mathrm{I}}_2}+\text{ White ppt. }\left[Y\right]$

    $\mathrm{NaI}+\left[\mathrm{Z}\right]$    colourless compound.

Here, compound [Z] :

Copper sulphate in reaction with potassium iodide gives following reaction,

$2{\mathrm{CuSO}}_4+4\mathrm{KI}\to 2\mathrm{CuI}+{\mathrm{I}}_2+2{\mathrm{K}}_2{\mathrm{SO}}_4$

Potassium sulphite is a white, water-soluble solid with the chemical formula${\mathrm{K}}_2{\mathrm{SO}}_4$.

It frequently serves as a potassium and sulphur source for fertilisers.

${\mathrm{I}}_2+{\mathrm{Na}}_2{\mathrm{S}}_2{\mathrm{O}}_3\to \mathrm{NaI}+{\mathrm{Na}}_2{\mathrm{S}}_4{\mathrm{O}}_6\text{ [colleurless compound.] }$

While ${\mathrm{Na}}_2{\mathrm{S}}_4{\mathrm{O}}_6$ (Sodium tetrathionate) is a colourless compound.