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On dissolving 0.5 g of a non-volatile non-ionic solute to 39 g of benzene, its vapor pressure decreases from 650 mm Hg to 640 mm Hg. The depression of freezing point of benzene (in K) upon addition of the solute is ____. (Given data: Molar mass and the molal freezing point depression constant of benzene are 78 g mol⁻¹ and 5.12 K kg mol⁻¹, respectively)

1. 1.0256
2. 1.026
3. 1.03
4. 1.04

Correct answer: 1.04

Solution

The depression in freezing point is calculated using the formula ΔTf = Kf × m, where m is the molality. Using the given data and solving for molality, the depression in freezing point is approximately 1.04 K.

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