${\mathrm{Cu}}^2+$ions Will be reduced to ${\mathrm{Cu}}^{+}$ions by the addition of an aqueous solution of:

The reactions takes place as,

$\begin{array}{r}2{\mathrm{Cu}}^{2+}+{\mathrm{SI}}^{-}\to {\mathrm{Cu}}_2{\mathrm{I}}_2\downarrow +{\mathrm{I}}_3^{-}\\ \text{ Whiteppt }\\ {\mathrm{Cu}}^{2+}+2{\mathrm{SCN}}^{-}\to \underset{\text{ Black ppt }}{\mathrm{Cu}\left({\mathrm{SCN}}_2\right)\downarrow }\end{array}$

Thiocyanogen and white copper (I) thiocyanate are generated when the precipitate progressively breaks down.

$2\mathrm{Cu}\left({\mathrm{SCN}}_2\downarrow 2\mathrm{CuSCN}\underset{\text{ White ppt }}{\downarrow }+(\mathrm{SCN}{)}_2\uparrow \right.$

${\mathrm{Cu}}^2+\text{ ions }$ Will be reduced to cu+ ions by the addition of an aqueous solution of KI, KSCN, KCN.