Match the term with the definition. match term definition atom a) a substance that cannot be broken down into a simpler substance element b) a tiny piece of matter particle c) a unique form of matter in which it can exist phase d) the basic unit of an element

A. Atom :- a substance that cannot be broken down into a simpler substance.

Explanation:

Atom is a basic unit of any chemical substance or element. It cannot be broken into simpler material.  Although it is known that an atom is made up of electron proton and neutron but these are not simpler substances. In an atom electron is negatively charged and proton is positively, while neutron is neutral.

real, smaller and upside-down.   so the answer should be b.