In the P - V diagram shown in figure, choose the correct options for the  process a - b

$\rho \propto \frac{1}{V}$

V is doubled so $\rho$ will remain half.

$U\propto T\propto pV$

According to given graph, $p\propto V$

$\therefore U\propto T\propto p^2 or V^2$

V is doubled, so U and T both will become four times.

$$\begin{gathered} p\propto V \\ \therefore \frac{T}{V}\propto V \\ \therefore T\propto V^2 \end{gathered}$$

$\left( \right.as\left.p\propto \frac{T}{V}\right)$

or T - V graph is a parabola passing through origin.