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

To solve the problem, we need to find the molecular weight of substance B based on the information given about the freezing points of the two solutions. We will use the concept of molality and the fact that the freezing points are the same.

### Step-by-Step Solution:

1. **Understanding the Problem**:
We have two solutions:
- A 3% (by weight) aqueous solution of A
- A 9% (by weight) aqueous solution of B
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