Three starts die and become deead stars. one of the theree becomes a neutron star, another becomes a black hole, and the third becomes white dwarf. which star, before it died, would have been the most massive and which star would have been the least massive?

Black hole most massive and white dwarf least massive should be correct. It really just depends on the original size of the star and it's gravitational pull pre death.

Explanation:

Just what I learned over time. I would still do more research on the subject though.