Capital gain which date to be consider

query is regarding that what date should be taken for calculation of sales consideration and for calculating indexation benefits

It's amply clear.

The date of sale is the date of transfer of capital asset.

Please do not reply to irrelevant queries. 

Rather than criticizing and giving unclear answer just reply date of agreement 31 Mar 21

as per section 2(47):-

(v) any transaction involving the allowing of the possession of any immovable property to be taken or retained in part performance of a contract of the nature referred to in section 53A of the Transfer of Property Act, 1882 (4 of 1882)

As per section 53A

Following conditions should be complied under Section 53A;

1. There should be a contract for consideration in writing and same should be signed by the transferor;

2. The contract should be for transfer of immovable property and from therein the term necessary to constitute transfer should be certainly ascertained;

3. The transferred should has taken possession of the property and has done something for furtherance of the contract;

4. The transferee should be ready and willing to perform his part of the contract; and

5. In this case even without execution of sale deed, the transferee acquires the right in the property and the transferor cannot claim any right in respect of property under consideration other than the rights expressly provided in the terms of contract.

In our case possession is handed over in Apr'21 and in the agreement also its mentioned that transaction will be treated as completed once the possession is given after full n final payment. 

Sabyasachi Mukherjee if u think query is irrelevent pls dont answer.

Nobody is forcing you to showcase your immense knowledge.