Solution:

• Measurement of osmotic pressure method is preferred for the determination of molar masses of macromolecules such as proteins and polymers.
• This is due to the following two reasons.
• The values given by the other colligative properties (elevation in the boiling point, the depression in the freezing point and relative lowering of vapour pressure) are so low that they cannot be measured accurately.
• Measurement of osmotic pressure is carried out at room temperature which does not require heating. Heating may change the nature of the polymer.