A(n) is a pure substance that can't be broken down into simpler substances by chemical or physical means. a. atom b. mineral c. chemical d. element

An element is a pure substance that can't be broken down into simpler substances by chemical or physical means. D
The element is a substance that can not be separated into smaller parts, while compound is a substance that can be decomposed.

An ELEMENT is a pure substance that can not be broken down into simpler substances by chemical or physical means. 
An element is homogeneous in nature, that is, it is made up of only one type of matter all through. There are different types of elements, some are gases, some are solids while some are liquids. Example of elements are: gold, silver, iron, sodium, calcium, hydrogen, oxygen, nitrogen, etc.