What mass of non-volatile solute (urea) needs to be dissolved in `100 g` of water in order to decrease the vapour pressure of water by `30%`. What will be the molality of solution?

Explanation

To solve the problem of finding the mass of non-volatile solute (urea) needed to decrease the vapor pressure of water by 30%, and to determine the molality of the solution, we can follow these steps:

### Step 1: Understand the Vapor Pressure Change
The initial vapor pressure of pure water (P₀) is assumed to be 100 atm. A decrease of 30% in vapor pressure means the final vapor pressure (Pₛ) will be:
\[ Pₛ = P₀ - 0.30 \times P₀ = 100 - 30 = 70 \text{ atm} \]

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