Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light, and electricity.

In a double displacement reaction such as the reaction between sodium sulphate solution and barium chloride solution:

(A) exchange of atoms takes place.

(B) exchange of ions takes place.

(C) a precipitate is produced.

(D) an insoluble salt is produced.

The correct option is:

Calcium oxide reacts vigorously with water to produce slaked lime.

${\mathrm{CaO}}_{\left(\mathrm{s}\right)}+{\mathrm{H}}_2{\mathrm{O}}_{\left(\mathrm{l}\right)} \to \mathrm{Ca}{\left(\mathrm{OH}\right)}_{2\left(\mathrm{aq}\right)}$

This reaction can be classified as:

(A) Combination reaction        (B) Exothermic reaction

(C) Endothermic reaction        (D) Oxidation reaction

Which of the following is the correct answer?

When hydrogen sulphide gas is passed through a blue solution of copper sulphate, a black precipitate of copper sulphide is obtained and the sulphuric acid so formed remains in the solution. The reaction is an example of a :