Electrolysis of water is the chemical reaction in which the decomposition of hydrogen and oxygen gases is carried by passing an electric current.
Following is the equation of electrolysis of water:
2H2O + Electrical energy → O2 + 2H2
The number of hydrogen molecules produced is thus twice the number of oxygen molecules. After electrolysis of water, hydrogen is collected at negative chose and oxygen is collected at the positive anode. Hydrogen is double in volume than oxygen.