Answer
The partial pressure of the helium gas is $354.85 $ torr.
Work Step by Step
We can use Dalton's Law of partial pressures to find the partial pressure the helium gas exerts by using the mole fraction and multiplying it by the total pressure. First we must determine the number of moles of each gas by taking the quantity and dividing by the molar mass of that gas. Then we must determine the fraction of helium gas compared to the total amount which is calculated by taking the moles of helium divided by the total number of moles of all the gases in the mixture
Number of Moles of He = $0.235 g\div4 = 0.05875 mols He$
Number of Moles of Ne = $0.325 g\div20 = 0.01625 mols Ne$
$He $ Mole Fraction = $\frac{0.05875 mols}{(0.05875 + 0.01625mols)} = 0.783333333$ Therefore, the $Partial Pressure = 0.783333333*453 torr = 354.85 torr$
