is it possible that we can use bitcoins in buying all commodities not only in one country but the entire wold? and how will this affect the economy.
Well, it's quite good idea. it can be possible when entire world accept Bitcoin as we know few country is not accepting Bitcoin. So, until the entire world doesn't accept either it is not possible.
Yes and no country would like it to be like that. Currency is the identity of the country and its people.