What is abnormal molar mass?

(N/A) Abnormal molar mass is defined as the molar mass of a substance that is either higher or lower than the expected (theoretical) value calculated based on its chemical formula.
This phenomenon occurs due to the association or dissociation of solute particles in a solution.
$1$. Association: When solute particles combine to form larger aggregates,the number of particles decreases,leading to a higher observed molar mass than the theoretical value.
$2$. Dissociation: When solute particles break apart into ions,the number of particles increases,leading to a lower observed molar mass than the theoretical value.
The extent of this deviation is expressed using the van't Hoff factor $(i)$.