Final answer:
The 8M☉ star will use up its nuclear fuel the fastest because massive stars burn through their fuel more quickly than less massive ones.
Step-by-step explanation:
The star that will use up its nuclear fuel the fastest is the 8M☉ star. In astrophysics, it is known that the more massive a star is, the faster it will consume its nuclear fuel. This is because massive stars are much more luminous and output a greater amount of energy, which causes them to burn through their nuclear fuel at a much quicker rate compared to less massive stars. Given the options (a. 1M☉ star, b. 2M☉ star, c. 4M☉ star, and d. 8M☉ star), we can determine that the 8M☉ star is the most massive and hence will evolve off the main sequence first, leading to a faster depletion of its nuclear fuel reserves.