What is the definition of a mole in chemistry?

A mole is defined as a unit used to express the amount of a substance, and it is specifically equal to 6.022 x 10²³ particles, which can be atoms, molecules, ions, or other entities. This number is known as Avogadro's number and serves as a bridge between the microscopic world of atoms and molecules and the macroscopic quantities we measure in the lab.

Understanding moles is crucial in chemistry because it allows chemists to count quantities of substances in a practical way. For example, when you deal with reactions, stoichiometry calculations often involve moles to determine how much of one reactant is needed to react with another.

The other choices pertain to different concepts in science. A mole is not a unit of length or temperature, as those relate to different measurements entirely. Moreover, while the atomic mass of an element is reflected in grams per mole, it is not the definition of a mole itself; rather, it describes the mass of one mole of that element, which can lead to confusion but does not capture the core definition of a mole.