Four gas cylinders containing He, N₂, CO₂ and NH₃ gases separately are gradually cooled from a temperature of 500 K. Which gas will liquify first?

(Given Tc in K $$-$$ He : 5.3, N₂ : 126, CO₂ : 304.1 and NH₃ : 405.5)

Which one is not correct mathematical equation for Dalton's Law of partial pressure? Here p = total pressure of gaseous mixture

where p_i = partial pressure of i^th gas

$${\chi _i}$$ = mole fraction of i^th gas in gaseous mixture where $${\chi _i}$$ = mole fraction of i^th gas in gaseous mixture

$$p_i^o$$ = pressure of i^th gas in pure state

A 10.0 L flask contains 64 g of oxygen at 27$$^\circ$$C. (Assume O₂ gas is behaving ideally). The pressure inside the flask in bar is (Given R = 0.0831 L bar K^$$-$$1 mol^$$-$$1)