Final answer:
The highest energy subshell among those listed is the 4s subshell, which gets filled with electrons immediately after the 3p subshell and before the 3d subshell according to electron configuration principles.
Step-by-step explanation:
Among the given subshells, the one that is highest in energy is the 4s subshell. According to the principles of electron configuration, after the 3p subshell is filled, electrons will fill the 4s subshell before the 3d subshell. This is because the 4s has a slightly lower energy than the 3d, despite what might be logically assumed from the principal quantum numbers alone. It is only after the 4s subshell is filled that electrons begin to occupy the 3d subshell. This pattern is reflected in the configuration of the periodic table and explains why for potassium (K), the electron configuration after [Ar] is 4s¹, with the next electron occupying the 4s subshell and not the 3d.