The limitations of Bohr's theory are:

i. A single line of hydrogen spectrum is found to be composed of severally closed packed. The origin of these lines of hydrogen spectra is not explained by Bohr.

ii. It fails to explain the splitting of spectral lines into very fine lines under magnetic field and eternal electric field.

In the case of filing of electrons into orbital having equal energies, called degenerate orbital. It states that "Electrons will distribute themselves in degenerate orbitals so as to give maximum multiply as much as possible."

Azimuthal quantum number (l) specifies the shape of orbital.

Quantum number: The atomic parameter which is used to describe the position and energy of an electron in an atom is called Quantum number.

In an orbit, the angular momentum is always quantized. Quantization means that a quantity can vary only discontinuously to get a specific value i.e. the orbits are possible only after a certain separation and they are not possible continuously.

Magnetic quantum number specifies the orientation of an orbital.

For 3^rd orbital,

The value of principle quantum number (n) = 3
The value of azimuthal quantum number (l) = 0 to (n-1) = 0, 1, 2

Magnetic quantum number represents the orientation of orbital in three dimensional spaces i.e. the number of orbital that are present for a particular value of principle quantum number.

The electron whose valence shell electronic configuration 4s² may be Calcium(Ca). The atomic number of calcium is 20. The electronic configuration of calcium is

Ca₂₀ = 1s², 2s² 2p⁶, 3s² 3p⁶, 4s²

The total number of p-electrons are 12.