Question

Which of the following orbitals has the lowest energy?
(A) 4d
(B) 4f
(C) 5s
(D) 5p

Answer 1

An atomic orbital is a mathematical function in atomic theory and quantum physics that describes the position and wave-like behaviour of an electron in an atom. This function may be used to determine the likelihood of locating any atom's electron in any given area surrounding the nucleus. The phrase atomic orbital can also refer to the actual region or space in which the electron can be calculated to be present, based on the orbital's mathematical structure.

Complete Step By Step Answer:
The energy necessary to take an electron present in an orbital to infinity, or the energy released when an electron is introduced to that orbital from infinity, is referred to as orbital energy. The energy of an orbital is determined by the principal quantum number (n) and the azimuthal quantum number (l), i.e. shell and subshells. It is the same for orbitals belonging to the same subshell, and degenerate orbitals are those with the same energy.
Multi-electron atoms, unlike hydrogen (single-electron atoms), exhibit varying energies in various subshells of the same shell. That is, for a given main quantum number, say 3, the energies of the various subshells 3s, 3p, and 3d will differ.
The existence of reciprocal repulsion among the electrons in multi-electron atoms explains why different energies exist between the various subshells of the same shell. The attractive force between the nucleus and electrons is much stronger than the repulsive forces between electrons in the inner and outer shells, which contributes to the multi-electron atom's stability.
The energy of orbitals is determined using n+l orbital values.
$4d=4+2=6$
$4f=4+3=7$
$5s=5+0=5$
$5p=5+1=6$
Hence 5s has the lowest energy
Option C is correct.

Note:
The outer shell electrons are unable to experience the full positive charge of the nucleus due to the existence of electrons in the inner shell. The shielding effect is the net nuclear charge felt by an outer shell electron, while the effective nuclear charge is the net nuclear charge felt by an outer shell electron.