Final answer:
The molar volume of CH4 and NH3 gases are the same at STP due to Avogadro's law. Both will occupy 22.4 liters per mole at STP, although they have different molecular weights.
Step-by-step explanation:
The molar volume of a gas at standard temperature and pressure (STP) is the volume one mole of the gas occupies under these conditions. According to Avogadro's law, equal volumes of all gases at the same temperature and pressure contain the same number of molecules. Therefore, at STP, one mole of CH4 (methane) and one mole of NH3 (ammonia) will occupy the same volume. For example, both will occupy 22.4 liters at STP. The difference between CH4 and NH3 is not in their molar volumes but in their molecular weights and structures. While CH4 has a molar mass of approximately 16.0 g/mol, NH3 has a molar mass of 17.0 g/mol.