Question

What is the ratio of densities of 2 gases, O2 & N2, having partial pressures in the ratio 2:3?

(a) 16/21

(b) 12/7

(c) 21/16

(d) 7/12

This question was addressed to me in a job interview.

I need to ask this question from Kinetic Theory topic in section Kinetic Theory of Physics – Class 11

Answer 1

The correct answer is (a) 16/21

Easiest explanation: The ratio of moles is the same as the ratio of partial pressures.

The ratio of densities:

d1/d2= (m1/V)/(m2/V)

= m1/m2= (n1M1)/(n1M2),

where n is the number of moles and M is the molecular mass.                                                                                                                                                                              d1/d2= (2/3)*(16/14)

= 16/21.