What do all pure substances have in common? a. they cannot be broken into smaller pieces. b. they are made up of atoms or groups of atoms. c. they cannot be mixed with other substances. d. they do not change in chemical reactions.

The correct option is B.

Explanation: Pure substances are defined as the substances which are made up of one one type of atom or a molecule. Example: Iron (Fe), etc.

Option A: These substances can be cut into smaller pieces because only the size of the substance is changing.

Option B: All the pure substances are made up of atoms and group of atoms known as molecules. So, this is common to all the pure substances.

Option C: These substances can be mixed with other substance. For example: Iron can be mixed with another Copper.

Option D: These substances when undergoing a chemical reaction will change its chemical composition.

Hence, the correct option is B.

- lead + phosphoric acid = hydrogen + lead(ii) phosphate