Give one example in case of the following reaction:
When an active metal displaces hydrogen from dilute sulphuric acid.

On heating blue-coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X are formed

(a) Write a balanced chemical equation of the reaction.

(b) Identify the brown gas X evolved.

(c) Identify the type of reaction

(d) What could be the pH range of aqueous solution of the gas X?

Give the characteristic test for the following gases.

(a) ${\mathrm{CO}}_2$

(b) ${\mathrm{SO}}_2$

(c) ${\mathrm{O}}_2$

(d) ${\mathrm{H}}_2$