JEE Main · 2021 · 17 Mar 2021 · Shift 2 · Heat & Thermodynamics

On any graph carrying $T$ as an axis an isothermal change holds $T$ fixed, so it must be the straight line perpendicular to the temperature axis. An adiabatic change of an ideal gas obeys $T{V}^{\gamma -1}=$ constant, so on a $V$–$T$ plot the volume falls as the temperature rises along a curve, and it obeys $P^{1-\gamma }{T}^{\gamma }=$ constant, so on a $P$–$T$ plot the pressure climbs steeply with temperature.
In the $P$–$V$ plot the vertical line is labelled adiabatic, but a vertical line there is a constant-volume change, and on a $P$–$V$ plot both an isotherm and an adiabat are falling curves; that plot is wrong. In the first $P$–$T$ plot the horizontal line is labelled isothermal, whereas an isotherm on a $P$–$T$ plot is vertical; that plot is wrong too.
The $V$–$T$ plot with the vertical isotherm and the falling adiabat, and the $P$–$T$ plot with the vertical isotherm and the rising adiabat, are drawn correctly: the diagrams labelled (c) and (d).