Taxation on property transaction

If a property is acquired by paying in installments,what is considered the date of acquisition for calculating capital gain out of booking,allotment letter,registration , possession letter or completion of payment. from the date of possession. Also can LT capital Gain from property be set off against the carried forward ST Capital Loss of shares. no.. Also if payment for a new residential property is being made currently, can proceeds of Long term Capital Gain from Shop be utilised to make remaining payments to save LT Tax liability. u can but condition is that before u have not any residential house . U can take NHA Bonds/ RECL bond for exemption.