Gold need to be mixed with other metals to make a ring? why?

Gold is not fully gold it's made up of other things and by adding those other metals it still isn't fully gold but it's much better and more furnished and stronger

First you need to some basics of chemistry. Gold as in pure gold is a metal that can be molded even by touch. Since it is soft goldsmiths add other metals(mainly copper) to make jewelry. By adding other metals it became an alloy and therefore becomes hard. To sum up, gold is mixed with other metals to retain its shape. Hope this helps!