Hi
You will be eligible to claim exemption of capital gains arising out of the sale of a flat.
However, please ensure that if you're not going to invest in another house immediately, then deposit the sale consideration into a Capital Gains Account Scheme in any bank. The deposit in the said account has to be made before the due date of filing the return of income (ie 31 July).
Happy to help you further, if need be.
Regards
Keerthiga