Capital gain

Why Not??? You can Ofcourse Sell Shares of Private Company for Consideration less than Book Value. Further, Since Shares being of Private Company are not listed in the Stock Exchange, STT are not paid on transfer. And you can set-off or Carry Forward the loss arising therefrom.

No actually, there is a provision in IFOS, Sec 56 where purchase of shares in consideration  below the FMV, difference would be taxable. (Aggregate Value exceeding Rs. 50,000).

So i just wanted to clarifyu whether there i any such provision in case of Sale of Shares?

Yeah, Difference between Sale Proceed and FMV of Shares, if exceeds 50000, then the diffence is taxable. But in your Query, you wrote Book Value instead of Fair Market Value.