[Use] Mixtures of solids or gases Mixtures in which the roles of solute and solvent are not clear [Concentration Type] 
Mole fraction
% c o m p o s i t i o n p p m p p b
M o l e f r a c t i o n
M o l a r i t y
M o l a l i t y
N o r m a l i t y
F o r m a l i t y