Which of the following statements about atoms is correct?

Atoms are the fundamental building blocks of matter and are considered indivisible in the context of standard chemical interactions. This means that when an atom exists as part of an element, it retains all properties of that element, such as reactivity, atomic mass, and valence. The structure of an atom, consisting of protons, neutrons, and electrons, defines its behavior in chemical reactions, and no further division is necessary or useful for understanding these properties. While atoms can be broken down in nuclear reactions or other extreme conditions, this does not pertain to their everyday classification in chemistry.

The other statements do not accurately reflect the nature of atoms. For instance, while atoms are present in living organisms, they are not the smallest units; molecules and compounds are formed from atoms, and these can exhibit properties that individual atoms cannot. Furthermore, atoms are not confined to solid substances; they exist in all states of matter—solid, liquid, and gas. Lastly, the idea that atoms can be divided while retaining their properties misrepresents what happens at the atomic level, as splitting atoms typically results in different particles with different properties.