$i\, = \,1\, - \,\alpha \,\left( {1 - \,\frac{1}{n}} \right)$
$0.9\, = \,1 - \,0.2\,\left( {1 - \frac{1}{n}} \right)$
On solving,
$\,\left( {1 - \frac{1}{n}} \right)\, = \,\frac{1}{2}$
$\frac{1}{n}\, = \,1\, - \frac{1}{2}\, = \frac{1}{2}$
$\therefore \,n = 2$
[આપેલ :દ્રાવ્ય $A$નું મોલર દળ $93\, g\, mol ^{-1}$. પાણીનો મોલલ અવનયન અચળાક $1.86\, K \,kg\, mol ^{-1}$ ]