Question

Which of the following is not a pure substance?
A) Oxygen
B) Carbon dioxide
C) Water
D) Milk

Answer 1

Actually milk is an impure substance because it is made up of several elements and minerals like water , carbohydrates,etc. But if not seen logically it is pure because we do not mix the minerals in it.

Answer 2

Pure Substances are made of the same material throughout and having the same properties intact. They cannot be separated into other substances.

Pure substances can be elements or compounds. Examples of pure substances  are carbon dioxide, water and oxygen . pure substances can be elements or compounds.

Milk is a blend of water, carbohydrates, fats, proteins and many other .Thus it is a mixture.The milk extracted from cows is a mixture of water, fat and milk solids. The milk solids are made of proteins and carbohydrates.