Sale of Commercial Property-Capital gains

one of our client is having a block of commercial (real estate) properties under 10% depreciation. He wants to dispose of one of the property. As per Sec 50 of IT Act, can we reduce the sale proceeds from the block so that there is not capital gains tax arises (the block value doesn't become nil)?

If the client doesn't want to reduce the fixed assets from the block, can we calculate capital gains as per normal properties (indexation and LTCG)?

Can someone throw light on this?