Question

what is an atom?
one of the states of matter
a type of energy
the tiniest building blocks that all matter is made of
the tiniest building blocks that all energy is made of

Explanation:

An atom is the basic unit of a chemical element. It is the smallest unit of matter that retains the properties of an element. States of matter (like solid, liquid, gas) are different forms matter can take, not what an atom is. Energy is not made of atoms. Atoms make up matter, not energy.

Answer:

The tiniest building blocks that all matter is made of.