The critical temperatures of O2,N2,H2. andCO2 are 154.3K,126K,33.2K and 304 K. The extent of adsorption on tungsten may be highest in case of

More easily liquefiable gases, (i.e., higher critical temperature) are readily adsorbed, as Vander Waal's forces are stronger near the critical temperatures. So. adsorption of CO2 will be highest.