Question

If an unknown substance CANNOT be broken down into simpler substances, it is

Answer 1

The correct answer is b. an element

The explanation:

when the ELEMENT is define as substance that cannot be decomposed (broken down) into simpler substances by ordinary chemical means. Examples: gold, iron, carbon, hydrogen, oxygen, nitrogen

Ex: diamond will be broken into carbon as well.

and SUBSTANCE: Material composed of only one kind of matter throughout (same atoms or same molecules).