you need to assess the market value of the property as on Apr 2001. you gave the option to choose the either the cost of the property or market value on Apr2001 and whichever is higher needs to be indexed. this indexed cost will be deducted from your sale consideration of 65lavs and balance will be taxable ad capital gains. you can invest the capital gains in capital gains tax bonds up to 50lacs for a period of 3years. else you need to invest entire sale consideration in a residential property and claim exemption on capital gains