Iron exhibits $$+2$$ and $$+3$$ oxidation states. Which of the following statements about iron is incorrect?

We compare the chemical behaviour of species derived from $$Fe^{2+}$$ (ferrous) and $$Fe^{3+}$$ (ferric). The decisive factor is the charge-to-radius ratio (polarising power) of the cation.

$$Fe^{3+}$$ has a higher charge and a smaller ionic radius than $$Fe^{2+}$$. Therefore it possesses:

(i) larger polarising power → compounds are more covalent, less ionic
(ii) stronger ability to interact with polar molecules such as $$H_2O$$ → easier hydrolysis
(iii) weaker basic character of its oxide (because covalent/acidic character grows with oxidation state)
(iv) higher volatility of its salts (greater covalent character favours sublimation/volatility)

Now examine each given statement.

Statement A: “Ferrous oxide is more basic in nature than ferric oxide.”
• Ferrous oxide $$FeO$$ (from $$Fe^{2+}$$) is more ionic than $$Fe_2O_3$$, hence more basic.
✓ Statement A is correct.

Statement B: “Ferrous compounds are relatively more ionic than the corresponding ferric compounds.”
• By Fajans’ rule, the lower charged and larger $$Fe^{2+}$$ forms more ionic compounds than $$Fe^{3+}$$.
✓ Statement B is correct.

Statement C: “Ferrous compounds are less volatile than the corresponding ferric compounds.”
• Ferric compounds are more covalent and therefore exhibit higher volatility; ferrous compounds (more ionic) are less volatile.
✓ Statement C is correct.

Statement D: “Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds.”
• Hydrolysis requires high polarising power; $$Fe^{3+}$$, not $$Fe^{2+}$$, fulfils this. Thus ferric compounds hydrolyse more readily.
✗ Statement D is incorrect.

Hence the incorrect statement is:

Option D which is: Ferrous compounds are more easily hydrolysed than the corresponding ferric compounds.