# A pale green crystalline metal salt $M$ dissolves freely in water. It gives a brown precipitate on addition of aqueous $NaOH$. The metal salt solution also gives a black precipitate on bubbling $H_2S$ in aqueous medium. An aqueous solution of the metal salt decolourises the pink colour of the permanganate solution. The metal in the metal salt solution is

(a) Copper
(b) Aluminium
(d) Iron

Pale green salt contains a mixture of $Fe^{2+}$ and $Fe^{3+}$ ions
$Fe^{3+} + 3OH^- \longrightarrow Fe(OH)_3$ brown ppt.
$Fe^{2+} + S^{2-} \longrightarrow FeS$ black ppt.
$Fe^{2+}$ reduces $KMnO_4$ discharging its pink colour.