JEE Main · 2018 · 08 Apr 2018 · Offline · Chemical Thermodynamics

Writing the van't Hoff relation as $\ln K=-\frac{\Delta H^{\circ }}{R}\cdot \frac{1}{T}+\frac{\Delta S^{\circ }}{R}$ shows that a plot of $\ln K$ against $\frac{1}{T}$ is a straight line of slope $-\frac{\Delta H^{\circ }}{R}$. For an exothermic reaction $\Delta H^{\circ }<0$, so this slope is positive and $K$ falls as the temperature rises. The lines carrying that positive slope are the pair marked A and B.