Final answer:
The statement is true; more massive stars are indeed hotter due to their stronger gravity enabling greater compression and hence more intense nuclear reactions, which result in higher luminosity and surface temperatures.
Step-by-step explanation:
The statement 'The more mass a star has, the hotter it is' is generally true. Massive stars have more gravity, which can compress their centers significantly, making them much hotter internally. This intense compression and heat facilitate vigorous nuclear reactions that produce a high energy flux, leading to greater luminosity and hotter surface temperatures. According to the Stefan-Boltzmann law, the energy flux from a blackbody, like a star, is proportional to the fourth power of its absolute temperature, implying that hotter stars emit significantly more energy.
Low-mass stars, in contrast, have lower gravity and thus are less compressed and cooler inside, making them less efficient at energy generation through nuclear reactions. Hence, they are less luminous and exhibit cooler surface temperatures. Our Sun, for instance, falls between these two extremes. Therefore, as stars with more mass are hotter, they shine with greater luminosity and have higher surface temperatures compared to their lower mass counterparts.