\( M n^{2+} \) compounds are more stable than \( F e^{2+} \) compounds towards oxidation to their \( +3 \) state,
because

Electronic configuration of \( M n^{2+} \) is \( 4 s^{0} 3 d^{5} \) :
\begin{array}{|l|l|l|l|l|}
\hline \( 1 \) & \( 1 \) & \( 1 \) & \( 1 \) & \( 1 \) \\
\hline
\end{array}
Electronic configuration of \( F e^{2+} \) is \( 4 s^{0} 3 d^{6}: \)
\begin{array}{|ll|l|l|l|l|}
\hline \( 1 \) & \( \downarrow \) & \( 1 \) & \( 1 \) & \( 1 \) & \( 1 \) \\
\hline
\end{array}
Since, in \( M n^{2+} \) the d-orbital is completely half-filled, therefore, its third ionization energy is high and hence, it stable
towards oxidation to \( +3 \) oxidation states, whereas, in \( \mathrm{Fe}^{2+} \), the d-orbital is partially filled and only one electron is paired,
therefore, its third ionization energy is lower than \( \mathrm{Mn}^{2+} \) ion and hence, it is less stable towards \( +3 \) oxidation states.