When a green iron salt is heated strongly, its colour finally changes to black and the odour of burning sulphur is given out.
$(a)$ Name the iron salt.
$(b)$ Name the type of reaction that takes place during the heating of iron salt.

(N/A) The green iron salt is Ferrous sulphate heptahydrate $(FeSO_{4} \cdot 7H_{2}O)$. Upon strong heating, it loses water of crystallization and then decomposes into Ferric oxide $(Fe_{2}O_{3})$, which is black in colour, along with sulphur dioxide $(SO_{2})$ and sulphur trioxide $(SO_{3})$ gases.
$(b)$ This is a thermal decomposition reaction because a single reactant breaks down into multiple products upon the application of heat.