Answer
(Fatwa: 212=214/B)
To exchange the currencies of a country with difference is not allowed. For example, to exchanging one dollar to two dollars, or giving one pound in exchange of two pounds is not allowed; since the currencies of a country are regarded as one jins (category/class). Yes, it will be right to exchange the currency of a country to the currency of another country with differences; since the currencies of different countries vary as per their standard, name, value and parts, so they will be considered as different categories and therefore exchanging them with difference will be allowed:
علة القدر مع الجنس فان وجدا حرم الفضل و النساء، وان عدما حلا ۔۔۔ (درمختار مع الشامي)
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband