A vessel of \( 25 \mathrm{~L} \) contains \( 20 \mathrm{~g} \) of i...

A vessel of \( 25 \mathrm{~L} \) contains \( 20 \mathrm{~g} \) of ideal gas \( X \) at \( 300 \mathrm{~K} \). The pressure exerted by the gas is \( 1 \mathrm{~atm} .20 \mathrm{~g} \) of ideal gas \( Y \) is added to the vessel keeping the same temperature. Total pressure became \( 3 \mathrm{~atm} \). Upon further addition of \( 20 \mathrm{~g} \) ideal gas \( Z \) the pressure became \( 7 \mathrm{~atm} \). Answer the following questions. (Hint: Ideal gas equation is applicable on mixture of ideal gases) [Take, \( \mathrm{R}=1 / 12 \mathrm{~L} . \mathrm{atm} / \mathrm{mol} \mathrm{K} \) ] Find the average molar mass of the mixture of gases \( \mathrm{X}, \mathrm{Y} \) and \( Z \).
(A) 40/7
(B) \( 50 / 7 \)
(C) 20
(D) \( 60 / 7 \)