Which is an example of using a physical property?

Correct answer: Separating iron with a magnet

The governing idea is that physical separation uses a physical difference without producing a new substance. Iron is attracted by a magnet, while many accompanying materials are not, so magnetic property can be used to remove iron from a mixture. This makes option A correct. Burning wood is a chemical change because new substances form. Making milk sour involves chemical transformations caused largely by fermentation, and rusting iron forms hydrated iron oxides through chemical reaction. In magnetic separation, the iron remains iron before and after the process; only its position in the mixture changes. Thus the example demonstrates the practical use of a physical property.