A real gas at T and V  behave ideally provides its van der waals constant $\mathrm{\alpha }$ is related to the constant b by the expression 

A real gas at T and V  behave ideally provides its van der waals constant $\mathrm{\alpha }$ is related to the constant b by the expression is  $a=RTb\left(\frac{V}{V-nb}\right)$

The amount of the attraction between gas molecules is represented by the Van der Waal constant 'a,' and the effective volume of the gas molecules is represented by the Van der Waal constant 'b'.

Hence the option (B) is correct.