Answer:
Given total pressure of the gas mixture(hydrogen and helium) is 2.99 atm
Number of moles of hydrogen is ---- 13.2 mol
Number of moles of helium is ---- 19.1 mol
Determine the partial pressure of the helium gas.
Ratio of effusion rates of the two gases.
Explanation:
According to Dalton's law of partial pressures,
partial pressure of a component gas in a mixture is:
partial pressure of a gas = total pressure x mole fraction
mole fraction of helium gas is:

Partial pressure of He gas is:

Effusion rate of a gas is inversely proportional to its square root of its molecular mass.

Hence, rates of effusion of H2:He is 1.414:1.