Among Fe^ 3+ , Pb^ 2+ , Cu^ 2+ and Mn^ 2+ , identify the one that...

The group reagent $H_2S$ in the presence of $NH_4OH$ is used for the precipitation of Group IV cations in qualitative analysis.

Among the given ions, $Mn^{2+}$ belongs to Group IV and is precipitated as $MnS$.

$Pb^{2+}$ and $Cu^{2+}$ belong to Group II and are precipitated by $H_2S$ in an acidic medium.

$Fe^{3+}$ belongs to Group III and is precipitated as $Fe(OH)_3$ by $NH_4OH$ in the presence of $NH_4Cl$.

The metal corresponding to the precipitated ion is Manganese ($Mn$).

The electronic configuration of $Mn$ is $[Ar] 3d^5 4s^2$. By losing all its valence electrons, it can exhibit a maximum oxidation state of $+7$ (for example, in $KMnO_4$).

Answer: $+7$