CBSE Class 10 Science 2020 · Paper 31/5/1 · Question 16(a)

(a) Oxygen is liberated at the anode (positive electrode) and hydrogen at the cathode (negative electrode). (b) One molecule of water contains two atoms of hydrogen and one atom of oxygen, so its decomposition gives two molecules of hydrogen for every molecule of oxygen, $2{\text{H}}_2\text{O}⟶2{\text{H}}_2+{\text{O}}_2$. Collected under the same conditions, the hydrogen therefore occupies twice the volume of the oxygen. (c) The electrolysis of water would not take place (practically no gas would be collected), because pure water is a very poor conductor of electricity; dilute ${\text{H}}_2{\text{SO}}_4$ provides the ions that let the current flow.