Capital Gain - Income Tax

A owns a site absolutely and the neighbouring site is owned by B absolutely. Both A and B give their sites for joint development to same builder. Under the advice of developer, the two sites are amalgamated so as to get more floor area. My query is whether any capital gain tax is attracted when two sites of A B are amalgamated. This is because when sites are amalgamated, A gets 50% right in site owned by B previously and vice versa. Does it amount to exchange and capital gain tax is payable. Invite experts opinion on this.