Google Play deducted extra Rupee 50 after first-time Play Store purchase of an App/Game. Why is that?
Don't worry Vinit, one of the standard way for payment gateways (including Google Checkout and PayPal, PaisaPay etc) to validate your account is by deducting a small amount (typically 1 USD or  an approximate equivalent 50 INR) and returning it in next few days. 

Please wait for few days and while doing so, please observe for any reversal of 50 INR. If you see a credit to your payment account then all fall in order.