Question

What do all pure substances have in common?
A.
They cannot be broken into smaller pieces.
B.
They do not change in chemical reactions.
C.
They are made up of atoms or groups of atoms.
D.
They cannot be mixed with other substances.

Answer 1

C. They are made up of atoms or groups of atoms.

Explanation: A pure substance (element or compound) has a definite composition and is composed of atoms or groups of atoms (molecules or ions). A is wrong because you can physically break a pure substance into smaller pieces; B is wrong because pure substances can undergo chemical reactions; D is wrong because you can mix a pure substance with others (though then the result is a mixture, not a pure substance).