Question

Nickel and gold combine to make white gold. White gold is considered a(n) of nickel and gold.

Answer 1

White gold is considered an alloy of nickel and gold.
Alloy is the term which refers to the combination of metals, in which a new type of a metal is created. When you mix gold and some other white metal (such as nickel, palladium, or manganese), you get an alloy known as white gold. 

Answer 2

I think metal combinations are called alloy