Proving using ideal gas law that molar volume at NTP is 22.4 litres
The issue is that one mole of a gas at NTP should not be 22.4 L based on the ideal gas. This is only true for a gas at STP. The key difference between the two conditions is they are defined by different temperatures (STP is for 273 K while NTP is for 293 K). 

They are also different in that the IUPAC now defines STP with respect to 1 bar while NTP is defined with respect to 1 atm. 

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