In the fourth group, white precipitate of $\mathrm{Mn}(\mathrm{OH}{)}_2$ on heating with ${\mathrm{PbO}}_2$ and concentrated  ${\mathrm{HNO}}_3$ gives red-violet (purple) colour due to the formation of :

In the fourth group, white precipitate of $\mathrm{Mn}(\mathrm{OH}{)}_2$ on heating with ${\mathrm{PbO}}_2$ and concentrated  ${\mathrm{HNO}}_3$ gives red-violet (purple) colour due to the formation of ${\mathrm{HMnO}}_4$.

The reaction is,

$$\begin{gathered} 5{\mathrm{PbO}}_2+2{\mathrm{Mn}}^{2+}+4{\mathrm{H}}^{+}⟶2{\mathrm{MnO}}_4^{-}+5{\mathrm{Pb}}^{2+}+2{\mathrm{H}}_2\mathrm{O} \\ \downarrow \\ {\mathrm{HMnO}}_4 \end{gathered}$$

The correct option is A.