(i) Compressibility factor (Z) of real gas cannot be unity, while compressibility factor for an ideal gas is one. (ii) At low pressure and high temperature a gas behaves more like an ideals gas, so the deviation is very less. (iii) Intermolecularforces among gas molecules are weak as compare to liquid and solid but, these forces cannot be zero. (iv) Ideal gas follows van der Waals' equation pV=nRT Gases which do not follow this equation are real gases. Therefore, statements(iii) and (iv) are incorrect.