(i) Van der Waal's constant 'a': Its value is a measure of the magnitude of the attractive forces among the molecules of the gas. Greater the value of 'a', larger are the inter-molecular forces of attraction.
(ii) Van der Waal's constant 'b': Its value is a measure of the effective size of the gas molecules. Its value is equal to four times the actual volume of the gas molecules. It is called excluded volume or co-volume.
