During electrolysis of water why does …

The chemical decomposition produced by passing an electric current through a conducting liquid is called electrolysis.

Take out carbon rods carefully from two discarded cells. Clean their metal caps with sand paper. Wrap copper wires around the metal caps of the carbon rods and join them to a battery. These two rods are electrodes.

Now, pour a cupful of water in a glass/plastic bowl and add a teaspoonful of salt or a few drops of lemon juice to water to make it more conducting.  Immerse the electrodes in this solution. Make sure that the metal caps of the carbon rods are outside the water. Wait for 3-4 minutes. We will see that the bubbles of gases are produced at the two carbon electrodes. The formation of gas bubbles at the two carbon electrodes shows that a chemical change has taken place in water on passing electric current through it.