Question bank/NEET UG/Chemistry

NEET UGChemistryModerateNEET 2025

5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 torr respectively. Which of the following is true regarding the described solution?

Show answer and solution
Sol. Ptotal=XXPX∘+XYPY∘P_{total} = X_XP_X^\circ + X_YP_Y^\circ

=515×63+1015×78= \frac{5}{15} \times 63 + \frac{10}{15} \times 78

=21+52= 21 + 52

=73= 73 torr

Observed total pressure of solution is 70 torr.


It is less than calculated total pressure.


Hence, it shows negative deviation.

Source: geekyrakshit/indian-exam-questions / neet2025-code45

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