The amount of margin available in your funds section under Available margin can be used to trade in F&O.
Available margin = Cash balance + Margin from shares - Used margin

When both cash and collateral margins are available, which one is utilized first? What is the order of utilization?
What is the margin blocking percentage during the end-of-expiry week for physical settlement of stock option contracts?
Can I do intraday trading in stock options?
When does expiry take place for Nifty, Bank Nifty, Sensex, Bankex, and stock option contracts?