Name the sodium compound which is used for softening hard water.

Name the acid and base from which the following salts have been formed:
$(i)$ Sodium acetate.
$(ii)$ Ammonium chloride.

$(a)$ Write the chemical name and chemical formula of washing soda.
$(b)$ How is it obtained from sodium chloride? Give equations of the reactions.
$(c)$ Why is it called a basic salt? Give any one of its uses.

State what happens when:
$(a)$ Hydrated copper sulphate is heated.
Also,write the chemical equation for the reaction.

Identify the correct representation of the reaction occurring during the chlor-alkali process.

What is the chemical formula of gypsum?