Mole fraction
The mole fraction (χ) of a component is the ratio of its moles to the total moles in the mixture. It's dimensionless and always between 0 and 1. The sum of all mole fractions equals 1.
χᵢ = nᵢ / (n₁ + n₂ + ... + nₙ)
Mole fractions are used in Raoult's Law, Dalton's Law of partial pressures, and ideal solution calculations.