Give reasons for the following:
a. Measurement of osmotic pressure method is preferred for the determination of molar masses of  macromolecules such as proteins and polymers.
b. Aquatic animals are more comfortable in cold water than in warm water.
c. Elevation of boiling point of 1M KCl solution is nearly double than 1M sugar solution.

(a) In osmotic pressure method, pressure is measured at room temperature and instead of molality, molarity of the solution is used. It is preferred for the macromolecules like proteins as they are unstable at high temperature and polymers have poor solubility. Also, due to their high molecular mass, the only colligative property which has a measurable magnitude is osmotic pressure. Therefore, osmotic pressure method is preferred.  

(b) In cold water, the solubility of oxygen is more. The amount of dissolved oxygen in water decreases with increase in the temperature of water. Therefore, aquatic animals are more comfortable in cold water than in warm water.  

(c) 1M KCl solution dissociates into 1M K⁺ and 1M Cl^- whereas 1M sugar solution does not dissociates to give ions. So, the Van't Hoff factor for KCl solution is 2 whereas that for sugar solution is 1. As we know, greater is the Van't Hoff factor, greater would be the colligative property. Hence, elevation of boiling point of 1M KCl solution is nearly double than that of 1M sugar solution.