Question

An___is matter that cannot be broken down into anything simpler by chemical reaction

Answer 1

An atom is matter that cannot be broken down into anything simpler by chemical reaction

Answer 2

Answer: element

Step-by-step explanation:

Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Copper
`Cu`

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: water
`H_2O`

`2H_2O\rightarrow 2H_2+O_2`

Thus as it given that it cannot be broken down into anything simpler by chemical reaction , it is an element.