What will happen if we dont sell stock option on ita expiry.?

what price will be deducted and credited to account

It really depends on the moneyness of the option, if its ITM and you decide to hold it to expiry, then you will get the intresic value of the stock minus STT. If the option expires worthless, you will lose the premium paid. This is assuming you are long. If you are short, the opposite is applicable. Check this https://zerodha.com/varsity/module/option-theory/