Capital gain on exchange on commercial property

The answer itself is very big, i am trying to explain in brief.

1stly try to recall or co relate with sec 54 and 54F. Hopefully now ur fog will be little clear.

2ndly as per sec 45(1) is the charging section of capital gain and it provides as under, any profits and gain arising from transfer of a capital asset effected in PY shall be chargeable to income tax under the head of capital gains in the yr in which transfer took place.

so, in ur example both the parties exchange there properties without any extra consideration.

Here as per income tax, exchange is also treated as transfer and stamp duty value will be the value of sale consideration. 

Now both the parties have to be calculate capital gain tax on the basis of section 48.

3rdly, in case of residential property(in ur case it is commercial property) govt has given relife on capital gain tax by investing amount as per sec 54 that specify, for

• individual/ HUF 
• Transfer of residential house
• and the consideration is invested in another house property in india either,
• Purchase one yr before the transfer or purchase two yr after the transfer or constructed three yr after transfer 
• If the capital gain<amt invested, so full amt will be exempt from capital gain.
• And if capital gain> amt invested, difference is taxable

In your case capital gain have to be calculated on the basis of stump duty value and cost of purchase.