Here is list of securities which are considered as cash equivalent.
Here’s a comparison between Liquid Funds and ETF’s: Liquid funds vs. Liquid ETF/Overnight Funds
Margin requirement depends on price and volatility of the security. Also, if your Option position is in loss, your margin requirement will increase as losses are marked to market and deducted actively from your available margin.
In case you don’t have sufficient margins, you’ll have to add more funds to ensure your position isn’t squared-off.
@siva-reddy can you.