Write an equation to show the reaction between Plaster of Paris and water.

$(i)$ Name the products obtained in the chlor-alkali process.
$(ii)$ Name the gases liberated at the anode and at the cathode,respectively.
$(iii)$ Name the solution which is used as raw material in this process.

$(a)$ Study the following chemical equation:
$CaSO_4 \cdot 2H_2O \xrightarrow{373K} CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O$
Name the reactant and the product. State one use of the product.

Sodium carbonate is a basic salt because it is a salt of :

$(i)$ What is meant by the term hydrated salt?
$(ii)$ Give two examples of hydrated salts that are white in color and state their chemical formulas.

The metal salt $A$ is blue in colour. When salt $A$ is heated strongly over a burner,a substance $B$ present in it is eliminated and a white powder $C$ is left behind. When a few drops of a liquid $D$ are added to powder $C$,it becomes blue again.
$(a)$ Identify $A, B, C, D$.
$(b)$ Write the chemical equations involved.
$(c)$ Give an example of a salt which also shows the above property.