text: The partial pressure of H2 is just the total pressure minus the partial pressure of Ne.  The ratio of the H2 part press and total press gives the mole fraction of H2.  \n\nNow just calculate the number of moles in your 421 mL using the ideal gas equation  PV = nRT.  Solve for n, multiply this by the mole fraction of H2 to get the moles of H2, then multiply this by the mole weight of H2.\n\nI'll let you do the math.