In the van der Waals equation for gases,what does the constant $b$ represent?

The unit of the Van der Waals constant '$a$' is .......

Assertion : Compressibility factor $(Z)$ for non-ideal gases can be greater than $1$.
Reason : Non-ideal gases always exert higher pressure than expected.

For one mole of a van der Waals' gas,the compressibility factor $Z = (pV/RT)$ at a fixed volume will certainly decrease,if
[Given : $a$ and $b$ are standard parameters for van der Waals' gas]

Which among the following statements is/are incorrect regarding real gases?
$(i)$ Their compressibility factor is never equal to unity $(Z \neq 1)$.
$(ii)$ The deviations from ideal behavior 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,$PV = nRT$.

The density of a gas $A$ at $1 \ atm$ and $750 \ K$ is $0.3 \ g/L$. If the molar mass of $A$ is $27 \ g/mol$,then choose the correct statement -