Three of the following four materials are alike in a certain way and one is different. Find the odd one out.

Examining the classification of each material:

Brass is an alloy composed of copper and zinc mixed together.

Iron is a pure metallic element.

Copper is a pure metallic element.

Silver is a pure metallic element.

Iron, Copper, and Silver are all pure elements found on the periodic table. They exist naturally as single elements.

Brass is fundamentally different as it is an alloy - a mixture of two or more metals (specifically copper and zinc). It is manufactured by combining elements rather than occurring as a pure substance.

Therefore, Brass is the odd one out.