Question

which of these is not an alloy? brass bronze stainless steel copper

Explanation:

An alloy is a mixture of two or more metals (or a metal and a non - metal). Brass is an alloy of copper and zinc. Bronze is an alloy of copper and tin. Stainless steel is an alloy of iron, chromium, nickel, etc. Copper is a pure metal, not a mixture of metals.

Answer:

copper