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
The number of moles of oxygen = 32/32
Total number of moles =2+1=3.
The mole fraction of oxygen =
The molar fraction is directly proportional to the total pressure exerted.
Hence, the required option is D