Well right now,we are not into EET method of taxation.So at the time of maturity,the entire amount of principal is exempt from tax.Only that part of interest will be taxed which you have already not taken into account on accrual basis in the previous years.And as you are getting the money at the time of maturity,so there is no question of any deduction under sec 80C either.But there will be no tax on the principal amount received on maturity.But things may change in future if the government switches to EET(exempt-exempt-taxed)method whereby deduction will be allowed on investment and the amount will be taxed on maturity.
