What is the definition of a mole in chemistry?

The mole is a fundamental unit in chemistry used to quantify the amount of substance. The correct definition states that a mole represents the amount of substance that contains as many elementary entities (such as atoms, molecules, ions, etc.) as there are atoms in exactly 12 grams of pure carbon-12. This definition is grounded in Avogadro's number, which is approximately (6.022 \times 10^{23}).

Carbon-12 is the standard used for defining the mole because it is a stable isotope and is abundant, making it a reliable reference point. When one mole of any substance is considered, it will contain Avogadro's number of entities, whether they are atoms in an elemental substance or molecules in a compound.

This concept is crucial because it allows chemists to relate macroscopic amounts of substances that can be measured in grams to the quantity of microscopic entities that take part in chemical reactions. Such a quantification is essential for stoichiometry, a foundational concept in chemical calculations.

The other definitions either misrepresent the number of entities involved, reference incorrect amounts or substances, or do not communicate the relationship to Avogadro's number effectively. Understanding the mole through the correct definition is critical for mastering stoichiometric calculations