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

Let as assume  32 g of oxygen be mixed with 32 g of methane.

The molar masses of methane and oxygen are 16 g/mol and 32 g/mole respectively

The number of moles of methane = 32/16

 =2 moles.

The number of moles of oxygen = 32/32

 =1mole.

Total number of moles =2+1=3.

The mole fraction of oxygen  = $\frac{1}{1+2}$

= 1/3

The molar  fraction is directly proportional to the total pressure exerted.

Hence, the required option is D