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The vapour pressure is least for?

1. pure water
2. \( 0.1 \mathrm{m} \) aqueous urea
3. \( 0.2 \mathrm{m} \) aqueous urea
4. 0.3m aqueous urea

Correct answer: 0.3m aqueous urea

Solution

Urea is a nonvolatile solute, so adding more of it lowers the vapour pressure of water by reducing the mole fraction of water. Therefore, the most concentrated urea solution has the least vapour pressure.

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