The given graph represent the variations of compressibility factor...

From the graph it is clear that the value of $Z$ decreases with increase of pressure. We can explain as follows on the basis of van der Waals' equation. At high pressure, when ' $P$ ' is large, $V$ will be small and one can not ignore ' $b$ ' in comparison to $V$. However, the term $\frac{a}{V^2}$ may be considered negligible in comparison to ' $p$ ' in van der Waals' equation or $$\begin{aligned}\left(p+\frac{a}{V^2}\right)(V-b) & =n R T \\ P(V-b) & =n R T \\ p V-p b & =n R T \\ \frac{p V}{n R T}& =1+\frac{p b}{n R T}\\ Z & =1+\frac{p b}{n R T} \end{aligned}$$ or Here, $Z$ is greater than one and it increases linearly with pressure. Hence, statement (b) is false.