A white chemical compound becomes hard on mixing with proper quantity of water. It is also used in surgery to maintain joints in a fixed position. Name the chemical compound.

A salt X when dissolved in distilled water gives a clear solution which turns red litmus blue. Explain the phenomenon.

A person found that the cake prepared by him is hard and small in size. Which ingredient has he forgotten to add that would have caused the cake to rise and become light? Explain your answer.

When chlorine and sodium hydroxide being produced during the electrolysis of brine are allowed to mix, a new chemical is formed. Name this chemical and write its uses.

Write the name and formula of one salt each which contains:

(a) twomolecules of water of crystallisation

(b) five molecules of water of crystallisation

(c) ten molecules of water of crystallization