Final answer:
The value of the principal quantum number for an electron in a 5d orbital is 5, meaning the electron is in the fifth energy level.
Step-by-step explanation:
The principal quantum number for an electron in a 5d orbital is 5. This number, denoted as 'n', indicates the energy level or shell in which the electron resides. In the case of a 5d orbital, the prime quantum number n corresponds to 5, implying that the electron is in the fifth energy level.
Additionally, the d subshell has a secondary quantum number, represented as 'l', which is equal to 2 for d orbitals. Therefore, a 5d orbital indicates that electrons are located in the fifth energy shell (n = 5) within its d subshell (l = 2), which can further be characterized by magnetic quantum numbers m₁ values of -2, -1, 0, +1, and +2.