Final answer:
The minimum possible speed for an electron depends on its energy level, but it will approach, without reaching, the speed of light as its kinetic energy becomes a significant fraction of its rest mass energy.
Step-by-step explanation:
The minimum possible speed for an electron can't logically be 0 m/s because even at rest, it has intrinsic quantum mechanical motion due to the Heisenberg Uncertainty Principle. However, for practical purposes outside of quantum mechanical contexts, electrons can momentarily appear to be at rest. The rest mass energy of an electron is 0.511 MeV, indicating that as an electron's kinetic energy approaches approximately 150% of the rest mass energy, it will travel at velocities close to the speed of light, though never reaching it due to relativity constraints. To say an electron's speed is the speed of light would violate fundamental principles of physics as only massless particles such as photons travel at the speed of light in a vacuum. So, the correct option addressing the minimum possible speed based on these facts is 'd', as it depends on the electron's energy level.