Final answer:
The highest sublevel after the 3p would logically be the 3d, but in fact, the 4s sublevel has a lower energy due to its orbital shape and proximity to the nucleus.
Step-by-step explanation:
Within each level of evidence in chemistry, particularly when discussing the energy of electron sublevels, the highest sublevel can vary depending on the principal energy level. But generally, the sublevel with the most complex orbital shapes, the d sublevel, would be expected to be the highest in energy after the p sublevel. However, in a surprising twist, the 4s sublevel is actually slightly lower in energy than the 3d sublevel. The reason for this is related to the specifics of quantum mechanics and the shape and penetration of the orbitals into the space closer to the nucleus. The 4s orbital has a higher probability of being closer to the nucleus where the attractive force from the positive charge is stronger, thus stabilizing the energy of the electrons in that sublevel.