Correct Answer: (c) Water
Solution:The most common form of copper sulphate is its pentahydrate, given by the chemical formula CuSO₄.5H₂O. It is a blue coloured chemical. When it is heated, the blue colour disappears and it turns white.
Heating removes the water of crystallization which is responsible for blue colour of the crystal. CuSO₄.5H₂O(Blue)---Heat → CuSO₄(White) + 5H₂O
After it cools, if a few drops of water are put into the test tube, the copper sulphate turns blue again as water of 1 crystallization make the copper sulphate hydrated again.