Check Statement I: $\mathrm{SbCl_5}$ vs $\mathrm{SbCl_3}$

By Fajan’s rule, for the same anion $\mathrm{Cl^-}$, a cation in higher oxidation state has greater polarising power and hence forms a bond with more covalent character.

• In $\mathrm{SbCl_3}$, antimony is in oxidation state $+3$.
• In $\mathrm{SbCl_5}$, antimony is in oxidation state $+5$.

Since $\mathrm{Sb^{5+}}$ polarises $\mathrm{Cl^-}$ more strongly than $\mathrm{Sb^{3+}}$, we get: $\mathrm{SbCl_5} \text{ is more covalent than } \mathrm{SbCl_3}$

So, Statement I is correct.

Check Statement II: Stability of higher oxides of halogens

Halogens form oxides in several oxidation states. In general, for halogens, oxides with higher oxidation states are more stable than those with lower oxidation states.

This is because halogens are highly electronegative and can stabilize higher oxidation states in oxides due to bonding with oxygen.

Examples support this trend:

• $\mathrm{Cl_2O}$ has chlorine in $+1$ oxidation state.
• $\mathrm{Cl_2O_7}$ has chlorine in $+7$ oxidation state and is a well-known stable higher oxide compared with lower oxides.

Hence, Statement II is also correct.

Choose the correct option

Since both Statement I and Statement II are correct, the correct option is: $\boxed{\text{A}}$