How many moles of Neon will be needed to fill a 48.0 Liter tank at STP?
The volume of one mole of any gas at STP is 22.4 L. STP means standard temperature and pressure.
This comes from Avogadro's hypothesis that equal volumes of gases at the same temperature and pressure contain equal numbers of moles. The value is arrived at by solving the ideal gas equation, PV=nRT, for the volume of one mole using standard temperature and pressure, P = 1.00 atm and T = 273 K.
We can use 22.4 L/mol as a conversion factor in this problem:
(48.0L) x 1 mol/22.4 L = 2.14 moles of neon
Notice that it doesn't matter what the gas is, this conversion factor works for all gases at STP that obey the ideal gas law.