Explain the concept of element.

Explanation

An element is defined as a pure substances. Which can neither be decomposed nor built from simpler substances by any physical or chemical method. Ex : `underset("mercuric oxide")(HgO_(s)) to underset("mercury")(Hg) + underset("oxygen")(O_(2)(g))`
Here mercuric oxide is a compound (`therefore` it decomposes).
but mercury and oxygen are element (`therefore` it does not decomposes).