Final answer:
A 0.5 solar mass main sequence star will appear less bright compared to a 4 solar mass main sequence star.
Step-by-step explanation:
A 0.5 solar mass main sequence star is less massive compared to a 4 solar mass main sequence star. It is a reasonably good approximation to say that luminosity (brightness) varies as the fourth power of the mass. So, the 4 solar mass star will be approximately 16 times brighter than the 0.5 solar mass star.