What do we call a substance that cannot be made by the combination of simpler substances or reduced to simpler substances?

The term for a substance that cannot be made by combining simpler substances or reduced to simpler substances is an element. Elements are the fundamental building blocks of matter, consisting of only one type of atom. Each element has distinct properties and can be found on the periodic table, where they are represented by their atomic symbols.

Compounds, on the other hand, are substances formed when two or more elements chemically combine in fixed proportions. Mixtures are combinations of two or more substances where each retains its own properties and can be physically separated. Solutions are a type of mixture where one substance (the solute) is dissolved in another (the solvent). Therefore, the defining characteristic of an element is that it remains indivisible into simpler substances by chemical means, making it unique within the classification of matter.