$3 / 8$

$8 / 3$

$2 / 3$

$3 / 2$

$\mathrm{Xe}>\mathrm{Kr}>\mathrm{Ar}>\mathrm{Ne}>\mathrm{He}$

$\mathrm{He}>\mathrm{Ne}>\mathrm{Kr}>\mathrm{Ar}>\mathrm{Xe}$

$\mathrm{Xe}>\mathrm{Ar}>\mathrm{He}>\mathrm{Ne}>\mathrm{Kr}$

$\mathrm{Ne}>\mathrm{Xe}>\mathrm{Kr}>\mathrm{He}>\mathrm{Ar}$

more the charge on the atom, more is its stability.

electronic configuration of $\mathrm{Fe}^{2+}$ is $3 d^6$ while that of $\mathrm{Fe}^{3+}$ is $3 d^5$.

$\mathrm{Fe}^{2+}$ has a larger size than that of $\mathrm{Fe}^{3+}$.

$\mathrm{Fe}^{3+}$ ions are coloured.