A mixture of He, Ar, and Xe has a total pressure of 3.00 atm . The partial pressure of He is 0.450 atm , and the partial pressure of Ar is 0.450 atm

A mixture of He, Ar, and Xe has a total pressure of 3.00 atm . The partial pressure of He is 0.450 atm , and the partial pressure of Ar is 0.450 atm . What is the partial pressure of Xe? A volume of 18.0 L contains a mixture of 0.250 mole N2 , 0.250 mole O2 , and an unknown quantity of He. The temperature of the mixture is 0 ∘C , and the total pressure is 1.00 atm . How many grams of helium are present in the gas mixture?