The answer is as :
The match will be as follows:
Atom - B) the basic unit of an element
Element - D)a substance that cannot be broken down into a simpler substance
Particle - A) a tiny piece of matter
Phase - C) a unique form of matter in which it can exist
So
atom is defined as the basic unit of an element .
Element is a substance that cannot be broken down into a simpler substance.
Particle is a tiny piece of matter.
Phase is a unique form of matter in which it can exist.