For BANKNIFTY the limit is 5000 in single order.
Market Lot size is 25, so in single shot you can buy 5000/25 = 200 lots
The maximum limit in a single order is called quantity freeze limit.
This is applied for all F&O contracts to ensure there is no wrong entry while entering positions.
The contract size for all scrips is provided here
May I know y r curious about the max quantity?
thanks a lot