What is the principal quantum number for a 3d orbital?

The principal quantum number is a key concept in quantum mechanics that indicates the energy level or shell of an electron in an atom. For atomic orbitals, the principal quantum number is denoted by the letter 'n'. It determines the size and energy of the orbital, with higher values of 'n' corresponding to orbitals that are further away from the nucleus and have higher energy.

In the case of a 3d orbital, the number '3' is the principal quantum number. This signifies that the electrons in the 3d orbital are located in the third energy level. The 'd' subshell implies that the electrons are in a specific type of orbital that has a more complex shape compared to s or p orbitals, primarily influencing how these electrons interact with other atoms.

Thus, since the 3d orbital belongs to the third energy level, the principal quantum number for a 3d orbital is indeed 3.