What is a mole in chemistry?

The concept of a mole in chemistry is defined as the amount of a substance that contains the same number of elementary particles (such as atoms, molecules, or ions) as there are in 12 grams of carbon-12. This count of particles is known as Avogadro's number, which is approximately 6.022 x 10²³. The mole serves as a bridge between the microscopic world of atoms and molecules and the macroscopic world of grams and liters, allowing chemists to count and react quantities of substances in a meaningful way.

This definition is fundamental in stoichiometry, enabling the calculation of reactants and products in chemical reactions based on their respective molar amounts. When one says they have one mole of water, for instance, they are referring to a quantity that contains exactly 6.022 x 10²³ water molecules.

In contrast, the other options describe related but specific aspects of the mole concept. One option mentions the mass of a mole of substance, which is related but doesn't define what a mole is. Another references the relationship between moles and molar mass, which is part of calculations but does not address the definition of a mole itself. Lastly, the volume occupied by one mole of gas at standard