Dear Vinod,
AS you mentioned that at the time of redevelopment flat was not sold to the builder. However it is very unlikely. We need to see the agreement between you and builder and related documents. If it was not sold to the builder what was the consideration for builder for redevelopment of houses? However for the time being i am assuming that it was not sale and based on that assumption question to your main answer is as follows:
Sale of flat in 2016 -
Sale of flat for Rs. 80 lacs will definitely attract capital gain taxes. However, your mother can avail exemption under section 54 for the amount of 30 lakhs invested in new house.
Calculation - Assuming spent of 10 lacs was in the year 1997-98
Sale consideration 8,000,000
Less brokerage - 80,000
reg. exp -20,000
Net sale consideration 7,900,000
Less Indexed cost of acq. -1,551,284
Indexed cost of improvement -1 -3,265,861
Indexed cost of improvement -2 -1,087,525
Capital Gain 1,995,330
Less Exemp[tion uinder section 54 -1,995,330
Taxable capital gain Nil
Feel free to get in touch with me in case you require any assistance.
Thanks and Regards,
Abhishek Dugar