I, II and III are three isotherms respectively at T1, T2 and T3 temperatures. The order of temperature will be
T1 =T2 = T3
T1 <T2 > T3
T1 >T2 > T3
T1 >T2 = T3
As the temperture increases at constant P, volume of gas increases.
The plots of intensity versus wavelength of three black bodies at temperatures T1,T2 and T3 respectively are shown in figure. Their temperatures are such that