What volume does a #"5.0-g"# sample of hydrogen gas occupy at STP?

The problem provides you with the molar volume of a gas at STP

#V_"n STP" = "22.4 L mol"^(-1)#

So, you know that under STP conditions for pressure and temperature, #1# mole of any ideal gas will occupy #"22.4 L"#.

You can use the molar volume of a gas at STP as a conversion factor to help you determine the volume a sample of gas will occupy when kept under STP conditions.

In your case, you need to find volume, so rearrange the molar volume of a gas as

#"22.4 L"/"1 mole H"_2 -># this takes you from moles of #"H"_2# to liters

Now, in order to find the number of moles present in #"5.0 g"# of hydrogen gas, you can use the gas' molar mass

#5.0 color(red)(cancel(color(black)("g"))) * "1 mole H"_2/(2.016color(red)(cancel(color(black)("g")))) = "2.48 moles H"_2#

This sample of hydrogen gas will thus occupy

#2.48 color(red)(cancel(color(black)("moles H"_2))) * "22.4 L"/(1color(red)(cancel(color(black)("mole H"_2)))) = color(darkgreen)(ul(color(black)("56 L")))#

The answer is rounded to two sig figs, the number of sig figs you have for the mass of hydrogen gas.