Can I have more clarification about this matter. Is it mandatory to recognize unrealized gain or loss in case of trading shares investment?

An unrealized gain is a  profit  resulting from an investment that  merely exists on paper.

 A gain becomes realized once the position is closed for a profit.

It is a profitable position that has yet to be sold in return for cash, such as a stock position that has increased in capital gains but still remains open.

Similarly ,same is the position for' unrealised loss'.

Therefore , it is not appropriate should any one take unrealised loss amount( short/long  term capital assets ) and take tax advantage by adjusting against  short/long term capital gains .