Though formally Bitcoin is not yet regularised properly across the globe, yet India is catching up with the Bitcoins.
I would like to know the list of all trusted site available for users to buy and sell Bitcoins in India.
You can buy bitcoins online from anywhere in the world. If you prefer to buy locally in your area in person you can find someone who is selling by going to this web site:
https://localbitcoins.com/Type in your city and do a search from there. I did a search on Mumbai and came up with several people there who sell bitcoins locally. The results in your city may vary.