Explain why $F{e}^{3+}$ is more stable than $F{e}^{2+}$ ion.

Atomic number of Fe-atom=26 and its electronic configuration: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{6}4s^2$
$\therefore$Electronic config. Of $F{e}^{2+}:1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^6$
and electronic config. Of $F{e}^{3+}:1s^{2}2s^{2}2p^{6}3s^{2}2p^{6}3d^5$
We know that the electronic configuration of half-filled or fully filled subshells are more stable compared to others. now, the 3d-subshells are more stable compared to other. now, the 3d-subshell of $F{e}^{3+}$ ion is exactly half-filled and hence $F{e}^{3+}$ is more stable than $F{e}^{2+}$.