Explanation

(c) The dotted line in the diagram shows that there is no derivation in the value of $\frac{pV}{nT}$ for different temperature $T_{1}\ and\ T_{2}$ for increasing pressure so, this gas behaves ideally. Hence, dotted line corresponds to ‘ideal’ gas behavior.
At high temperature, the derivation of the gas is less and at low temperature the derivation of gas is more. In the graph, derivation for $T_{2}$ is greater than for $T_{1}$. Thus,
$T_{1} > T_{2}$
Since, the two curves intersect at dotted line so, the value of $\frac{pV}{nT}$ at that point on the $y$-axis is same for all gases.