A minimum of Rs 500 has to be deposited in the PPF account every year. If you do not do this, the account becomes inactive. With this, you cannot make new deposits and do not get the full benefit of compound interest.
To activate the account, an application has to be made to the bank / post office, for the number of years the account has been inactive, a minimum deposit of ₹50 (penalty) of each year + ₹500 of the current year. After that, your account will be reactivated.