(a) Ferrous sulphate crystals are green in colour but their colour changes to white when heated. This is because the water in the crystals evaporates and anhydrous ferrous sulphate is produced, changing the colour of the crystals from light green to white.

(b) When anhydrous sulphate is heated to a high temperature, it decomposes to produce the ferric oxide, sulphur dioxide, and sulphur trioxide. This is a decomposition reaction.