The orbital angular momentum of a $3p$ electron is

In a multi-electron atom,which of the following orbitals have the same energy in the absence of magnetic and electric fields? $(a) n = 1, l = 0, m = 0, (b) n = 3, l = 0, m = 0, (c) n = 2, l = 1, m = 1, (d) n = 3, l = 2, m = 1, (e) n = 3, l = 2, m = 0$

Which electronic configuration for oxygen is correct according to Hund's rule of maximum multiplicity?

The order of increasing energies of the orbitals follows:

The electronic configuration of the valence shell of $Cu$ is $3d^{10}4s^{1}$ and not $3d^{9}4s^{2}$. How is this configuration explained?

What is the electronic configuration of $Cu^{2+} (Z = 29)$ in its ground state?