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The vapour pressure of two liquids ‘P’ and ‘Q’ are 80 and 60 torr, respectively. The total vapour pressure of solution obtained by mixing 3 mole of ‘P’ and 2 mole of ‘Q’ would be

1. 72 torr
2. 140 torr
3. 68 torr
4. 20 torr

Correct answer: 72 torr

Solution

The total vapour pressure is calculated using Raoult's law: P_total = (X_P * P_P) + (X_Q * P_Q). Mole fractions are X_P = 3/(3+2) = 0.6 and X_Q = 2/(3+2) = 0.4. Substituting, P_total = (0.6 * 80) + (0.4 * 60) = 72 torr.

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