How is nifty and banknifty option strike range determined each day?

I can see on the nse option chain website and on a few brokers that today the nifty option trading range is from 14150 to 18050 even though many of these strikes are not liquid. (I am not talking about strikes allowed for buying by zerodha due to member level oi restriction). I want to know in general for trading how this range is determined by NSE. Also, few days ago the lower bound was around 13750 and upper bound around 17500. Now today since the lower bound has moved to 14150, what happens to people who have positions in strikes below 14150. @siva

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If any positions are there they can continue to hold, also don’t think if any OI is there on that particular strike they will remove it. They do this certain intervals based on some internal methodology, mostly volatility will be considered and also levels of underlying.

Adding to Siva.

You can refer to this article on NSE website.

As explained there, at a time there can only be 30 ITM, 1 ATM and 30 OTM strikes for Index Options. The strikes available will be based on previous day’s closing price.