Compare $\mathrm{Fe^{2+}}$ and $\mathrm{Fe^{3+}}$

Iron commonly shows two oxidation states:

• Ferrous: $\mathrm{Fe^{2+}}$
• Ferric: $\mathrm{Fe^{3+}}$

Since $\mathrm{Fe^{3+}}$ has higher positive charge and smaller effective ionic size, it has:

• greater polarising power
• more covalent character in compounds
• greater tendency to hydrolyse

Check option A

A: Ferrous oxide is more basic in nature than the ferric oxide

$\mathrm{FeO}$ contains $\mathrm{Fe^{2+}}$, while $\mathrm{Fe_2O_3}$ contains $\mathrm{Fe^{3+}}$.

Lower oxidation state oxides are generally more basic, and higher oxidation state oxides are less basic / more amphoteric.

Therefore, $\mathrm{FeO} \text{ is more basic than } \mathrm{Fe_2O_3}$

So, A is correct.

Check option B

B: Ferrous compounds are relatively more ionic than the corresponding ferric compounds

Because $\mathrm{Fe^{3+}}$ has higher charge density, it polarises anions more strongly, making ferric compounds more covalent.

Hence ferrous compounds are indeed more ionic than corresponding ferric compounds.

So, B is correct.

Check option C

C: Ferrous compounds are less volatile than the corresponding ferric compounds

More ionic compounds generally have:

• stronger electrostatic attraction
• higher melting/boiling points
• lower volatility

Since ferrous compounds are more ionic than ferric compounds, they are generally less volatile than corresponding ferric compounds.

So, C is correct.

Check option D

D: Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds

Hydrolysis is greater for cations with higher charge density and stronger polarising power.

Since $\mathrm{Fe^{3+}}$ has higher charge density than $\mathrm{Fe^{2+}}$, ferric compounds are more easily hydrolysed than ferrous compounds.

Therefore the statement in D is incorrect.

Conclusion

The incorrect statement is: $\boxed{\text{D}}$