Final answer:
A substance that can be broken down into simpler components by chemical means is a compound. Compounds are made of two or more elements chemically bonded and can be chemically decomposed, unlike elements, which are the simplest pure substances and cannot be chemically broken down.
Step-by-step explanation:
If a substance can be broken down into simpler components by chemical means, it belongs to the category of compounds. Elements are pure substances that cannot be chemically broken down into simpler substances, as they are made of a single type of atom. On the other hand, compounds consist of two or more elements that are chemically combined in fixed ratios and can be decomposed into these constituent elements through chemical reactions. Mixtures, which include both heterogeneous and homogeneous mixtures (solutions), can be physically separated into their individual components without breaking them down chemically.
For example, compounds like water or table sugar (sucrose) are composed of two or more elements chemically bonded together and can be broken down into these simpler elements. Elements such as mercury or selenium, can't be broken down further chemically since they are composed of identical atoms.