Mole fraction refers to the fraction of a component in a solution when the amounts (component and solution) are expressed in moles. In other words, Mole fraction of a component is the ratio of moles of that particular component to the total moles of the solution.
ntot = Mole of the solution
Suppose a solution contains 3 components (two solutes, A and B, and a solvent C)
nC = Mole of component C
ntot = nA + nB + nC
Therefore above equation can also be written
Since value of mole fraction is obtained by dividing mass of a component by total mass of solution, it dimensionless. However, sometimes it is written as mole/mole.
𝒳A + 𝒳B + 𝒳C = 1
In contrast to density, Mole fraction is independent of temperature i.e., if temperature changes, the value of Mole fraction does not change.