Final answer:
Pure substances, which include compounds and elements, can only be separated into simpler substances by chemical means. Elements are indivisible by such means, while compounds can be decomposed back into elements through chemical reactions.
Step-by-step explanation:
Substances that can be separated into simpler substances only by chemical means are pure substances, specifically compounds and elements. Elements such as iron, silver, and oxygen are pure substances that cannot be broken down into simpler substances by chemical changes. Compounds, like table salt (sodium chloride), consist of two or more elements chemically combined in a fixed ratio and can only be separated into their elemental parts by chemical reactions.
Various techniques can be used to determine whether a substance is pure, including assessing melting and boiling points or using chromatography. Pure substances have sharp melting and boiling points, whereas impure substances have a range of temperatures over which they change state. Chromatography can separate substances based on differences in their chemical properties, indicating purity if only one substance is detected at the end of the process.