Solve this:
At moderate pressure, the compressibility factor for 1 mole of gas can be given by:
$$\begin{gathered} \left(1\right) 1-\left(\frac{RTV}{a}\right) \left(2\right) 1+\left(\frac{a}{RTV}\right) \\ \left(3\right) 1+\left(\frac{Pb}{RT}\right) \left(4\right) 1-\left(\frac{a}{RTV}\right) \end{gathered}$$