The freezing point of a `3%` (by weight) aqueous solution of `A` is equal to the freezing point of `9%` (by weight) aqueous solution of `B`. If the molecular weight of `A` is `60`, then the molecular weight of `B` will be
a`191` ,b.`90` , c.`45` , d.`20`

Explanation

a. Freezing point of aqueous solution of `A` =Freezing point of water -`DeltaT_(f)` of solution `A`
Freezing point of aqueous solution of `B` =Freezing point of water -`DeltaT_(f)` of solution `B`
As freezing point of aqueous solution of `A`
=Freezing point of aqueous solution of `B`
`:. DeltaT_(f)` of solution `A` =`DeltaT_(f)` of solution `B`
`K_(f)m=K_(f)m'`
`(3//60)/97 xx 1000=(9// Mw_(B) xx 1000)/91`
`:. Mw_(B)=191`