Boyle's law states that $P \propto 1/V$ at constant temperature. Thus, a plot of $P$ vs $1/V$ should be a straight line passing through the origin with a slope equal to $nRT$. As temperature $T$ increases, the slope $nRT$ increases. Therefore, for $T_3 > T_2 > T_1$, the slope of the line for $T_3$ is the steepest. Graph (2) correctly represents this relationship.