20 g of a binary electrolyte (Molecular mass =100) are dissolved in 500 g of water. The freezing point of the solution is `-0.74^(@)C` and `K_(f)=1.86` K kg `mol^(-1)`. The degree of ionisation of eletrolyte as :

Options

A. 0.5
B. 0.75
C. 1
D. zero

Answer

D

Explanation

`Delta T =(100 xx K_(f) xx 20)/(M_(2) xx W_(1))`
`:. 0.74 = (1000 xx 1.86 xx 20)/(M_(2) xx 500) :. M_(2) =100` `
Now ("normal molar.mass")/("exp.molar mass") = 1 + alpha, `
`:. 100/100 = 1 + alpha :. alpha = 0`