a
Steeper curve $(B)$ is adiabatic
Adiabatic $\Rightarrow \mathrm{PV}^{\prime}=$ const.
Or $\mathrm{P}\left(\frac{\mathrm{T}}{\mathrm{P}}\right)^{\mathrm{r}}=$ const.
$\frac{\mathrm{T}^v}{\mathrm{P}^{v-1}}=\text { const. }$
Curve $(A)$ is isothermal
$\mathrm{T}=$ const.
$\mathrm{PV}=$ const.