(i) If the molar mass calculated by using any of the colligative properties to be different than theoretically expected molar mass.
(ii) Extent of dissociation or association or ratio of the observed colligative property to calculated colligative property.
Detailed Answer:
(i) When the molar mass calculated with the help of colligative property, is different from theoretical molar mass, it is called as abnormal molar mass.
(ii) The ratio of the observed (experimental) value of a colligative property to the normal (calculated) value of the same property is called as van't Hoff factor (i).
