Explanation

• When equal masses of methane (CH4) and oxygen (O2) are mixed, the number of moles of each gas is equal. Since the molar mass of methane (16 g/mol) is smaller than that of oxygen (32 g/mol), the number of molecules of methane is greater than the number of molecules of oxygen.
• Let's calculate the fraction of total pressure exerted by oxygen:
• Number of moles of methane = Number of moles of oxygen (since equal masses are mixed)
• Molar ratio of methane to oxygen = 1:1
• Total pressure = Partial pressure of methane + Partial pressure of oxygen = 1 (due to methane) + 1 (due to oxygen) = 2
• Fraction of total pressure exerted by oxygen = Partial pressure of oxygen / Total pressure = 1 / 2 = 2/3