(A) Hydrogen gas at high pressure and low temperature does not behave as an ideal gas, so Z=1. The van der Waal's equation is (P+Vm2an2)(Vm−b)=nRT
At high pressure, the term an2/Vm2 can be ignored in comparison to value of P.
Therefore, the equation reduces to P(V−nb)=nRT
(B) For H2 gas at pressure =0 atm, the gas behaves as ideal gas,
so value of Z=1 at P=0 and it increases continuously on increasing P.
The ideal gas equation is obeyed, so PV=nRT.
(C) CO2 molecules have larger attractive forces under normal conditions.
The gas is at temperature, close to its liquefaction temperature, so deviation from ideal gas behaviour is high.
(D) At very large molar volume Z is not equal to 1 , instead Z=PVm/RT.