Upon expiry if your Option expires Out of the Money it expires worthless, and it it expires In The Money is settled at the Intrinsic Value.
Eg. Suppose you bought Nifty 11300 CE and Nifty on expiry day closed at 11500, your Option will be in the money and it will be settled at Intrinsic Value, which will be 200 (11500 - 11300).
P/L in this scenario will be the difference between the price you bought at and price it is settled at.
Eg. You bought this Option at 100 and it expired at 200, your profit will be 100 * 75 = 7500 (- Brokerage and other charges).
Now the same option 11300 CE, if Nifty on the expiry day closes at 11100, your option will expire worthless (at value of 0).
Here since the Option expired worthless you will lose the entire premium you paid, say it was 100 * 75, so 7500 will be your loss (+ Brokerage and other charges).
Yes. When your Option position expires ITM, extra STT of 0.125% is charged on the Intrinsic Value, this is only for options which are left to expire, if you square-off your position there is no additional STT.
To give you an example, take the 11300 CE which expired ITM with Intrinsic Value of 200, additional STT for this Option if you leave it to expire will be 18.75 (200 * 0.125 / 100 * 75) (75 is Nifty’s Lot Size).
You can learn more about this here.
There aren’t any other tax traps, you can calculate Brokerage and all other charges here.
Also you can view full list of charges here.
I’d also like to suggest you to read through Varsity, there is Options trading module which will teach you everything that you want to know about Options.