Not: atoms The answer is an element
Element
If an unknown substance cannot be broken down into simpler substances it is made of one kind of atom and an element.
Element
yes it is true
cannot be broken down into simpler substances by chemical means
No.An elementcan't be broken down into a simpler substance, without changing its chemical nature.
Substances that cannot be chemically broken down into simpler substances are called elements.
An element.
That would be an Element.
A substance that cannot be broken down is a pure substance
An element is a pure substance that cannot be broken down into simpler substances by chemical means.