Which of the following gases would deviate most from ideal gas behaviour at high pressure and low temperature?

Gases deviate from ideal behaviour when intermolecular forces are significant and molecular volume is not negligible. Carbon dioxide (CO₂) has stronger intermolecular forces (due to its larger molecular size and polarity) compared to the other gases listed. Helium and hydrogen, being small and non-polar, behave most ideally. CO₂ is most easily liquefied, indicating greatest deviation.