The solutions containing 6 g of urea (molecular mass =60) per `dm_(3)` of water and another containing 9 g of solute A per `dm^(3)` of water freeze at the same temp. The molecular mass of A is

Options

A. 12
B. 90
C. 54
D. 150

Answer

B

Explanation

Molality of urea solution =`6/(60 xx 1kg)=0.1M`
"As freezing point of both the solution are same they must have same molalities".
"Hence for solute A",
`"Molecular mass"="mass"/("molality" xx 1 kg)=9/(0.1 xx 1 )=90`