Options Contracts on Index and Individual Securities Final Exercise Settlement Closing price of such underlying security (or index) on the last trading day of the options contract.

If you calculate simple 1 closing average of underlying (without weightage, which is a tedious process, since we wont have all ticks etc…) it will be much closer to actual weighted average closing. (may be a +/- 0,02% ).

I am not sure if I understand teh last part about the weighted average, for instance nifty today closed at 11275, will the calculation for today’s weekly nifty expiry for 11200 CE , use that as the price or will it be something else
?

@sohnythomas It’s the final closing price for the day. Like today it’s 11257. So 11275 is the last traded price for the day whereas 11257 is the weighted average price as well as closing price for the day

What is the risk free rate that we should consider to calculate the option pricing or IV (other than last day of expiry) ?
a) 0.01% as a nominal rate because we are not loosing any opportunity cost for money in trading account.
b) 10% as considered by NSE ?
c) State Bank Saving Interest Rate @ 3.50%
d) Government Bond 1 Year Rate @ 6.25%

What is the risk free rate that we should consider to calculate the option pricing or IV ( last day of expiry) ?

If not getting down to complexity of calculations of average price, just add a 30 day Simple moving average line on 1 minute chart, the result would be exactly same.

nifty closing price and settlement price are more or less same today at 11980. What will be the settlement price of 11950 call option that also expired today?

Right, but one should also take STT into account, STT will be around 14 to 15 points so in this case it would not make sense to exercise it and better to let it go off.

The final closing price for the day is Weighted Average Price of the last 30 minutes of trading. You can read this post to know how Weighted Average Price is calculated.