Final answer:
The hottest and most luminous stars belong to spectral type O, while the coolest and least luminous stars are of spectral type M. The luminosity changes more significantly than mass from spectral types O to M.
Step-by-step explanation:
The hottest stars are those of spectral type O, which have the highest surface temperatures. O-type stars are also the most luminous due to their large mass and high temperature, emitting more light and energy than stars of other spectral types. In contrast, the coolest and least luminous stars are those of spectral type M, which have lower temperature and mass. As stars progress from spectral type O to type M along the main sequence, their luminosity changes by a larger factor than their mass, which means the amount of light and energy a star emits changes more dramatically than the star's actual weight.