Thought you want Airtel - Facebook free browsing (free basic) then read this

Using Facebook on your mobile phone will not result in data charges from Airtel unless you view content from other websites (for example, links to articles or YouTube videos). By signing up for this experience, you grant Facebook permission to tell others about your use of Facebook free of charge on the Airtel network. Facebook may also share other information with your network (including any of its group companies) about your use of Facebook's services, including information such as your phone number or data usage, in order to enable us and your operator to understand your use of the services. You also grant Airtel permission to give Facebook periodic access to your phone number, load balance and promo balance.
Source - Facebook T/C