Follow the idea
The mole connects the microscopic world of atoms and molecules to measurable laboratory amounts. One mole contains exactly the Avogadro constant number of specified entities. It is chemistry’s counting unit: like a dozen, but designed for unimaginably small objects. Stoichiometry turns a balanced chemical equation into a quantitative relationship between reacting species. The coefficients are ratios of entities or amounts of substance; they are the bridge from a symbolic reaction to laboratory quantities.
Primary references
IUPAC Gold Book · NIST · BIPM