What does the term “basic unit of matter” refer to?

a.) atoms
b.) elements
c.) molecules

The correct answer is A) Atoms.

Atom is considered as the smallest unit of matter. This is because atom can not be further divided into any smaller form using chemical means.

This was first explained by Dalton's atomic theory. According to this theory, matter is composed of atoms, which can not be divided further and so they are indestructible.

Thus, A) Atoms is the right answer.