Equal masses of methane and oxygen are mixed in an empty container

Equal masses of methane and oxygen are mixed in an empty container at 25°C. The fraction of the total pressure exerted by oxygen is

  1. 1/2
  2. 1/3
  3. 2/3
  4. (1/3) * (273/298)

Answer

Let the mass of methane and oxygen be m gm.

Mole fraction of oxygen, xO2 = m/32/(m/32 +m/16) = 1/3

Let the total pressure be P.

Partial pressure of O2, pO2 = P × xO2 = P x 1/3 = P/3

The correct option is B.