A fixed mass of an ideal gas is contained within a cylinder fitted with a frictionless piston, ensuring that the pressure of the gas remains constant. The density ρ \rho\,ρ of the gas is measured at various absolute temperatures TTT. Which of the following graphs will show a straight line passing through the origin?
ρ\rhoρ plotted against TTT
ρ\rhoρ plotted against T−1T^{-1}T−1
ρ\rhoρ plotted against T2T^2T2
ρ\rhoρ plotted against T−2T^{-2}T−2