d
The slope of straight line can't be tve. since, $\mathrm{T} \propto \mathrm{PV}$ and if slope is $+ve$, then both $\mathrm{P}$ and $\mathrm{V}$ are increasing. Therefore, temperature will always increase.
$\mathrm{T}_{1}<\mathrm{T}_{2}<\mathrm{T}_{3}<\mathrm{T}_{4}$
Thus, from graph it can be seen, that temperature first increases and then decrease.
