Hydrogen and helium are ideal gases at room temperature and ordinary pressure but sulfur dioxide is not an ideal gas?
H2 and He are ideal at room temperature because room temperature is very high for both of them so at high temperature gasses bahaves ideally due to the small force of attraction but in case of SO2 and CL2 room temperature is not so high for them so they have greater force of attraction between them and thus behaves non-ideally .......!