The correct answer is: A. A molecule
Avogadro’s hypothesis states that equal volumes of all gases, at the same temperature and pressure, contain the same number of molecules. This means that the smallest particle of an element or a compound, that can exist independently, is called a molecule.
A molecule is a group of two or more atoms held together by chemical bonds. Atoms are the basic units of matter and the fundamental particles of chemistry. They are the smallest particles that can exist independently and still retain the chemical properties of the element they belong to.
Cations are positively charged ions, while anions are negatively charged ions. They are formed when atoms lose or gain electrons. Cations are attracted to anions, and they form ionic bonds with each other. Ionic bonds are strong chemical bonds that are formed between oppositely charged ions.
The answer to the question is not B, C, or D because molecules are the smallest particles of an element or a compound that can exist independently. Cations and anions are not the smallest particles of an element or a compound, and they cannot exist independently.