(C) The green colour of the salt fades and a gas with the smell of burning sulphur is evolved.
When FeSO₄ is heated, it decomposes into Fe₂O₃, SO₂, and SO₃. The green colour fades (Fe²⁺ → Fe³⁺ forming red-brown Fe₂O₃) and SO₂/SO₃ gases produce the characteristic smell of burning sulphur. This is directly described in Activity 1.5 of Chapter 1.