Which one is an example of heterogenous catalysis?

Oxidation of sulphur dioxide into sulphur trioxide in the presence of oxides of nitrogen.
Combination between dinitrogen and dihydrogen to form ammonia in the presence of finely divided iron.
Decomposition of ozone in presence of nitrogen monoxide.
Hydrolysis of sugar catalysed by \( \text{H}^+ \) ions.

Correct answer · Option 2

Combination between dinitrogen and dihydrogen to form ammonia in the presence of finely divided iron.

In Haber's process, reactants are gases and the catalyst (iron) is solid, representing heterogenous catalysis.