On heating the blue solid, hydrated copper (II) sulphate, ______ is given off: -
A. $N{O_2} $
B. Steam
C. $HCl$
D. Oxygen

Hint: The chemical formula of the compound will be $CuS{O_4}.5{H_2} O$. This compound contains water of crystallization and since we are providing heat to the compound, the compound will split and the water molecule will be given off. Hence this reaction is called a dehydration reaction.

Complete Step by step answer:
When we heat the blue solid, hydrated copper (II) sulphate, steam is given off and the white solid of anhydrous copper (II) sulphate is formed. When the white solid is cooled and water added, blue hydrated copper (II) sulphate is reformed i.e. a reversible reaction.
We will now write the complete balanced equation of the reaction taking place: -
$CuS{O_4}.5{H_2} O\left (s \right) \to CuSO\left (s \right) + 5{H_2} O\left (l \right) $
When you heat hydrated copper (II) sulphate, it first loses two water molecules upon heating at $63^\circ C$ followed by two more at $109^\circ C$ and the final water molecule at $200^\circ C$ .The liquid droplets can be seen on the inner upper side of the test tube during the heating process of hydrated copper (II) sulphate which is due to the water of crystallization. It is white in colour at this stage.

So, the correct option will be option B. i.e. Steam.

Additional information: Copper (II) sulphate are the inorganic compounds with the chemical $CuS{O_4}{\left( {{H_2}O} \right)_x}$ , where $X$ can range from 0 to 5. The pentahydrate $(X = 5) $ ,is the most common form. Older names for this compound include blue vitriol, bluestone, vitriol of copper, and Roman vitriol. The pentahydrate $CuS{O_4}.5{H_2} O$ the most commonly encountered salt and is bright blue. It exothermically dissolves in water to give the aquo complex ${[Cu{({H_2}O)_6}]^{2 + }}$, which has octahedral molecular geometry.

Note: The hydrated copper (II) sulphate is Blue crystalline granules or powder and blue colour is due to the water of crystallization. This reaction is known as the dehydration decomposition reversible reaction because water is being released when the reaction is in forward direction to form the white solid and water is being added (rehydration) when the reaction is taking place in backward direction to reform the blue crystals.