16. Define ‘mole fraction’ of a substance in a solution.

Mole fraction: Commonly used symbol for mole fraction is x and subscript used on the right hand side of x denotes the component.
It is defined as:
Mole fraction of a component =

$\frac{\mathrm{Number} \mathrm{of} \mathrm{moles} \mathrm{of} \mathrm{the} \mathrm{component} }{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{moles} \mathrm{of} \mathrm{all} \mathrm{the} \mathrm{components}}$

For example, in a binary mixture, if the number of moles of A and B are nA and nB respectively, the mole fraction of A will be
 
x =$\frac{{\mathrm{n}}_{\mathrm{A}}}{{\mathrm{n}}_{\mathrm{A}} + {\mathrm{n}}_{\mathrm{B}}}$