what will happen if buyer not close position at the expiry day

[ShubhS9]

Explained here:

What happens if I don't square off my positions in options?

Index Options (Nifty and Bank Nifty, Nifty Financial Services) are cash-settled. If your Option expires OTM, it expires worthless. ITM Options are settled at their Intrinsic Value. And depending on your Profit/Loss money will be credited to / debited from your account. Also, if your Long Option position expires ITM, exchange will levy STT at 0.125% on the intrinsic value. There will be no STT on the Short position as STT is already paid when you sell the option. More details here: Sto…