The formula of iron (III) sulphate is

1. Fe₃SO₄
2. Fe(SO₄)₃
3. Fe₂(SO₄)₃
4. FeSO₄

Fe₂(SO₄)₃

Reason — Chemical formula of iron (III) sulphate:

$\text{Fe}^{3+} \space \text{SO}$4^{2-} \\[1em] \overset{\phantom{22}{3}}{\text{Fe}} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{SO}4} \Rightarrow \underset{\phantom{2}{2}}{\text{Fe}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{2}{3}}{\text{SO}4} \\[1em] \text{Fe}2\text{(SO}4)3

∴ Chemical formula of iron (III) sulphate is Fe₂(SO₄)₃