Question

An unknown substance is made only of identical atoms that cannot be broken down. This substance is a ________.

Answer 1

The substance is an element off of the periodic table. 

Answer 2

Answer: Element

Step-by-step explanation:

Element is a pure substance which is composed of identical atoms. It can not be decomposed into simpler constituents using chemical reactions.Example: Silver
`(Ag)`

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: carbon dioxide
`(CO_2)`

Thus an unknown substance is made only of identical atoms that cannot be broken down is an element.