How is option expiry price calculated if no buyers in Stock Short call option on expiry day

For the scenario where

Example: IDEA CELLULAR DEC 70 CE option writing is done at 5 RS. and at the end of Dec series expiry IDEA closed at 85, if there are no buyers or sellers how is the Option Assignment exercised. how will the price be calculated, what would be the penalty calculation.


Idea Dec 70 CE is in-the-money if Idea equity closes at 85. Since you have written the call at Rs.5, you will receive this premium. If Idea closes at 85, at expiry - your option value will be Rs.15 and your loss will be Rs.10(Multiplied by quantity) plus taxes and brokerage. STT is charged only in the sell side and since you have sold first, STT is already paid. In this case, there will be no STT penalty.


What if any option buy/sell expires ATM?
I’ll get money or loose. please explain me both scenarios of buy and sell