Capital gain tax

Dear Sir,
One of My Client is having Residential Property (row block) and Now he had converted into Commercial Property by constructing Shop on the same and want to sale the shop , proceeds arising from sale shop is to be utilised for purchase of residential property

My Question

1. whether capital Gain Tax is applicable on conversion of Residential Property into Commercial Property by constructing Shop 

2 Wat will be cost of acquisition on sale of Shop ( Cost of Residential Property )

3 Whether Indexetion benefit will be available

4  Also Purchase of Residential Property from sale proceeds of Shop, Whether deduction will be available from capital gain arising from sale of shop