I now see what satyenveshi was referring to. It is not s. 50C but is s. 50D which reads as follows:
So, the consideration being received by you i.e. the value of the 20 flats are not capable of being ascertained. So, the FMV of the land will be taken to be the consideration.
Quote"50D. Fair market value deemed to be full value of consideration in certain cases.—
Where the consideration received or accruing as a result of the transfer of a capital asset
by an assessee is not ascertainable or cannot be determined, then, for the purpose of
computing income chargeable to tax as capital gains, the fair market value of the said
asset on the date of transfer shall be deemed to be the full value of the consideration
received or accruing as a result of such transfer."
So, the consideration being received by you i.e. the value of the 20 flats are not capable of being ascertained. So, the FMV of the land will be taken to be the consideration.