In the fourth group, $Mn(OH)_2$ on heating with $PbO_2$ and conc. $HNO_3$ gives pink colour due to the formation of

Question

(a) $KMnO_4$
(b) $K_2MnO_4$
(c) $Pb(MnO_4)_2$
(d) $PbMnO_4$