Long term capital gains tax on sale of residential flat.

Capital gain without indexation works out to be 13 lacs (from the info). Since the asset is held for >36 months before sale, it shall be considered as long term asset and indexation needs to be done for computation of gain. Gain after considering indexation can be invested in bonds (u/s 54EC) in order to claim exemption.

I agree with Poornima, You can invest Only Gain i.e around Rs. 5.00 Lacs and can save whole tax. Further If you have not any other taxable income in this period, you can also claim Rs. 2,50,000/- which is basic exemption limit, available .