$A$ hydrogen atom has only one electron,so mutual repulsion between electrons is absent. However,in multielectron atoms,mutual repulsion between the electrons is significant. How does this affect the energy of an electron in the orbitals of the same principal quantum number in multielectron atoms?

(N/A) In a hydrogen atom,the energy of an electron depends only on the principal quantum number $(n)$.
In multielectron atoms,the presence of other electrons causes shielding and repulsion,which makes the energy of an electron dependent on both the principal quantum number $(n)$ and the azimuthal quantum number $(l)$.
According to the $(n+l)$ rule,for a given principal quantum number $(n)$,the energy of orbitals increases as the value of $l$ increases.
Therefore,in multielectron atoms,the orbitals of the same principal quantum number $(n)$ have different energies,following the order $E_s < E_p < E_d < E_f$.