How is a mole defined in chemistry?

A mole is defined as a quantity that contains Avogadro's number of particles or entities, which is approximately (6.022 \times 10^{23}). This fundamental concept in chemistry provides a bridge between the atomic scale and the macroscopic scale, allowing chemists to count and measure substances in a practical way.

When dealing with chemical reactions, solutions, or any scenario requiring a precise amount of substances, using moles enables accurate stoichiometric calculations—laying the groundwork for predicting the outcomes of reactions based on the quantities involved. As such, the mole is essential for quantifying how many atoms, molecules, ions, or formula units are present in a given sample, thus facilitating a deeper understanding of material properties and behaviors in chemical contexts.

The other choices offer definitions that are not aligned with the standard definition of a mole. For instance, volume pertains to the spatial capacity of a substance, mass relates to the amount of matter in a sample, and temperature indicates the thermal state of a material—none of which capture the unique concept that a mole represents in chemistry.