Final answer:
A 25 solar mass star likely loses more than the 45% mass loss experienced by stars that become white dwarfs, with the exact amount depending on the end-of-life supernova event. During the main sequence, mass loss due to fusion is not significant.
Step-by-step explanation:
The fraction of mass that a 25 solar mass main-sequence star ejects into space during its lifetime depends on whether it will end its life as a white dwarf or undergo a more dramatic end like a supernova. Stars with masses up to about 8 solar masses are predicted to lose enough mass to become white dwarfs, shedding approximately 45% of their initial mass. However, more massive stars, like a 25 solar mass star, are likely to lose a significant part of their mass in a supernova explosion, which can exceed this percentage. Additionally, during their main-sequence lifetime, stars convert about 10% of their hydrogen into helium, and a tiny fraction of this mass is lost as energy according to Einstein's mass-energy equivalence principle (E=mc^2). Figuring for Yourself indicates that during the main-sequence, the mass of a star does not change significantly, which would suggest that the mass loss during the main sequence is minimal in comparison to the total mass of the star.