Assertion :When small amount of an acid or base is added to pure water its pH undergoes a change. Reason: Addition of an acid or a base increases the degree of ionisation of water.
When small amount of an acid or base is added to pure water its pH undergoes a change.If we add acid the pH will become less than 7 and if we add base pH will be more than 7.
Addition of an acid or a base do not increases the degree of ionization of water.
So Assertion is correct but Reason is incorrect.
Hence option C is correct.