Arpan wrote :-
if I marry a French girl in France then after how long I will get citizenship and will I be able to work in any EU country?
You do actually ask two questions there. Firstly citizenship ... you will need to check the laws of the country in which you will be living.
Work in any EU country? Well actually any EEA country? Assuming the marriage is real .... not a marriage of convenience .... you might be entitled to an EEA Family Permit and that gives you the right to live and work. So, for example, you marry your French fiancée and the two of you live in Belgium. Your wife (as she will be) is exercising her treaty rights to live and work in another EEA country. You have the same rights as soon as the marriage happens, but need an EEA Family Permit in your passport to prove it.