Final answer:
The believed maximum mass a star can have is about 150 solar masses, which corresponds to option C. Stars may have initial masses greater, but due to mass loss, such massive stars are extremely rare.
Step-by-step explanation:
Among the options provided, the closest to the maximum mass a star is believed to have is about 150 solar masses. This is because stars are known to come in a wide range of masses, ranging from as little as 1/12 of the Sun's mass to those that are extraordinarily massive. While there are stars with masses up to about 100 times that of the Sun, only a very small number of stars, just a few out of several billion, may reach masses as large as 250 solar masses. However, it's been recognized that due to mass loss through various processes during their lifetimes, even these massive stars might not retain all their initial mass. The most massive stars may start with exceptionally large masses but can lose a significant portion by the time they end their lives.
Hence, the correct choice that represents the believed maximum mass of a star would be about 150 solar masses (option C), as stars with initial masses in excess of this figure are incredibly rare and seldom observed.