1.20 understand the term molar volume of a gas and use its values (24 dm3 and 24,000 cm3) at room temperature and pressure (rtp) in calculations.

Molar Volume Gases

One mole of any gas has a volume of 24 dm3 (24,000 cm3) at RTP

Volume of gas (dm3) = amount x 24 

Volume of gas (cm3) = amount x 24,000

Amount (mol) = volume of gas (cm3) / 24,000

NB -  if the volume is in cm3 then use 24,000 in your calculations and vice versa.