JEE Main · 2019 · 12 Jan 2019 · Shift 2 · States of Matter

For isothermal expansion of an ideal gas $PV$ stays constant, so $P$ against $V$ is a rectangular hyperbola, $P$ against $\frac{1}{V}$ is a straight line through the origin, and the internal energy, depending only on temperature, stays flat against $V$. The two plots that violate these $-$ the mis-drawn $P$ versus $\frac{1}{V}$ behaviour and the one showing $U$ rising with $V$ $-$ are the ones that do not represent isothermal expansion.