Choose the odd one out :

The correct option is B Copper

Copper is pure metal.

But steel, bronze and brass are metal alloy.

Steel is an alloy of iron and carbon, and sometimes other elements.

Brass is an alloy of copper and zinc.

Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive, but sometimes with other elements such as phosphorus, manganese, aluminium, or silicon.

Hence, option B is correct.