Which of the following materials fall in the category of a pure substance? (a) Ice (b) Milk (c) Iron (d) Hydrochloric acid (e) Calcium oxide (f) Mercury (g) Brick (h) Wood (i)Air

Answer: The following are pure substances among the nine compounds listed.

• Ice, iron, hydrochloric acid, calcium oxide, and mercury are pure substances since their composition is known.
• Milk is a colloid that behaves like a heterogeneous combination and hence isn’t a pure substance.
• Because brick and air are made up of multiple components, they do not come into the category of pure substances.