Which of the following is a mixture

A aluminum

B BaSO3

C Milk

D table salt

Answer is: C Milk.

Mixture is composed of at least two substances.

Milk is composed of water, proteins, sugars (mainly lactose) and fats.

Composition of milk can vary, for example, milk with 1% and milk 3% fats.

Other examples are pure substances.

Aluminium is chemical element, BaSO3 and table salt are chemical compounds.

Pure substance is made of only one type of atom (element) or only one type of molecule (compound), mixtures and solutions are made from two or more types of pure substances.