The mother tongue of india is hindi .english is read by almost indian to express their opinion in other country or other state because english made a global language which is is known by all and make easily understand.the learnig of english is just like a chalange for indian.
I should say that you are just plain stupid, from where you learned that Hindi is the mother tongue of India,Hindi is just one of the languages spoken in India and we do not have a national language. If you do not know that we have 22 languages which have legal status,we are a diversified nation with many languages and each and every state has its own language.
What you are saying is true but if you know Hindi language then you can survive in India in any state. Their may be lot of languages in India but Hindi is very common language which is spoken in all parts of India. But if anyone is able to read and work in Internet then their wont be problem for them to know English.