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.
Actually, bitcoin is already used by the world community. But it depends on each country that receives cryptocurrency (Bitcoin), some countries use bitcoin as a transaction tool and some use bitcoin as a medium of exchange only.