What are the exemptions available commercial property

Hello, I've sold an office space this FY. The office space was originally bought in 1997-98. Since I'm too old, I've given some mo I had bought an office space in 1996-1997 and sold it in 2017-2018. I have some questions around capital gains. I've got the property valued as on 2001-2002 and will index it further. 1. Since I'm too old I've given some money from the sale of office space to my son to purchase his first house. And he has bought a house within 3 months from the sale of office space. Will this be considered as an investment and exempted from capital gain. If not, what is the remedy? 2. What can I include in 'cost of improvement' of the office space I've sold? Can I add AC, partitions, cabins, cabinets, tables, chairs, etc? 3. Sr. Citizens have don't have to pay income tax against income upto 3 lacs. Can I save capital gains tax on 3 lacs or will that also be taxed and there is no exemption under income tax slab? If this exemption is available, can I also claim addl. 3 lacs in my wife's name as the property was jointly purchased by myself and my wife. Thank you,