Q.What is meant by molar volume of a gas ?

Because it is often far more convenient to measure the VOLUME of a gas than to weigh its mass, chemists rely on a consequence of Avogadro's law: at a given temperature and pressure, one mole of ANY gas — regardless of its identity — occupies exactly the same volume. At standard temperature and pressure (STP, historically taken as 0°C and 1 atmosphere), this molar volume works out to 22.4 dm3 (22.4 litres) per mole. (IUPAC's more recent STP convention, using 1 bar of pressure instead of 1 atmosphere, gives a very sligh …