How much Margin will be blocked if I buy an option?

Margin will be blocked as per premium paid for buying the option and the lot size of the contract.
For e.g. If Nifty 26-Jun-2014 CE7500 is quoting at 100, then the margin blocked for this option will be (100*50) = 5000.
Margin blocked will be displayed in Start -> Reports -> Margin Stmt -> Margin Usage Details (B)