Homogeneous catalysis is the process in which reactants, products and catalyst are in the same phase. So (iii) is the correct option.

In Heterogeneous catalysis, reactants, products, and catalyst are in a different phase. It is a process which occurs at the interface. So (ii) is wrong.

Crystallisation also occurs at the interface where solid substance gets crystallized at liquid interface.

Therefore, option (i) is wrong.

Conversion of metal into metal oxide at the interface of metal occurs during the corrosion process. So (iv) is also not correct.