According to Avogadro's Law, equal volumes of all gases at the same temperature and pressure contain the same number of molecules.

• A. False
• B. Only for ideal gases
• C. True
• D. Depends on pressure

Answer: (C)

Avogadro's law states that at the same temperature and pressure, equal volumes of gases contain the same number of particles. This comes from the idea that the amount of gas, measured in moles, is directly proportional to volume when T and P are fixed. Since the number of molecules N equals the amount in moles n times Avogadro's number, equal volumes contain the same N as well. The identity of the gas doesn’t matter, which is why different gases occupy the same volume per mole under those conditions. In practice, this is exact for ideal gases and is a very good approximation for real gases at moderate pressures; deviations appear at very high pressures or very low temperatures. So the statement is true because volume, at fixed T and P, scales with the amount of gas, independent of the type of gas.