I am an Indian and now in Hungary. How much euro's can I carry with me in flight when I travel back to India?
As much as you'd like. But, if it's a real lot, you might need to declare it.
amounts exceeding EUR 10,000.- or more or the equivalent in another currency (incl. banker's draft and cheques of any kind) must be declared.
amounts exceeding USD 5,000.- (or equivalent) in cash, or USD 10,000.- (or equivalent) in traveller's cheques must be declared; Local currency (Indian Rupee-INR): Import of INR is prohibited, except for residents of India importing up to INR 7,500.-
Foreign currencies include currency notes, traveller's cheques, cheques, drafts etc.
Edit: for future readers, make sure to check when this answer was updated last as I personally expect these numbers to be lowered soon-ish.