Dear Madam,
1. You will be liable to pay capital gain tax on the difference of sale value and indexed cost of acquisition. It will be a long term capital gain.
2.If the sale consideration is less than the stamp duty value. stamp duty value will be deemed to be sale consideration.
3. Refer point 1.
Please feel free to call/revert in case of any doubts
Thanks and Regards
Abhishek Dugar
CA CS B.Com