The colligative properties of electrolytes require a slightly different approach than the one used for the colligative properties of non-electrolytes. The electrolytes dissociate into ions in a solution. It is the number fo solute particles that determines the colligative properties of a solution. The electrolyte solutions, therefore, show abnormal colligative properties. To account for this effect we define a quantity called the van't Hoff factor, given by :
`i=("Actual number of particles in solution after dissociation")/("NUmber of formula units initially dissolved in solution")`
`i=1` (for non-electrolytes) ,
`i gt 1` (for electrolytes, undergoing dissociation)
`i lt 1` (for solutes, undergoing association).
The molare mass of the solute sodium hydroxide obtained from the measurement of the osmotic pressure of its aqueous solution at `27^(@)C` is `25 "g mol"^(-1)`. Therefore, its dissociation percentage in this solution is :

Options

A. 75
B. 60
C. 80
D. 70

Answer

B

Explanation

`i=("Normal molar mass")/("Abnormal molar mass")`
`alpha=(i=1)/(n-1)`
`i=1+alpha` for binary electrolyte
`:. 1 + alpha = (40)/(25), alpha = 0.6`
% ionisation = 60]