The gaseous mixture used for welding of metals is

Among the gases a, b, c , d, e and f, the gases that show only positive deviation from ideal behaviour at all pressures in the graph are

Which among the following statements is/are incorrect regarding real gases?

(i) Their compressibility factor is never equal to unity (Z $$\ne$$ 1).

(ii) The deviations from ideal behaviour are less at low pressures and high temperatures.

(iii) Intermolecular forces among gas molecules are equal to zero.

(iv) They obey van der Waals’ equation, $$pV = nRT$$

Among the following the maximum deviation from ideal gas behaviour is expected from