Structure Of Atom

Hund's rule states that electrons occupy degenerate orbitals (orbitals with the same energy) singly first, with parallel spins, before pairing begins.
This minimizes electron repulsion and stabilizes the atom.
Hence, Hund's rule governs the distribution of electrons in degenerate orbitals such as the , , or subshells.

- Aufbau principle explains the order of filling orbitals.
- Pauli exclusion principle states that no two electrons in the same atom can have all four quantum numbers identical.
- Planck’s theory deals with quantization of energy, not electron configurations.

The correct option is (C): Hund's rule

In quantum mechanics, the azimuthal quantum number defines the shape of the orbital and is associated with the angular momentum of an electron in an atom. For a given principal quantum number , the azimuthal quantum number can take integer values from 0 up to . That is: So if , then can be 0, 1, or 2.

The correct answer is option (A): to

Niels Bohr was awarded the Nobel Prize in Physics in 1922 for his contributions to the understanding of atomic structure and quantum theory.
Thus, the correct answer is Physics.

The maximum number of electrons that can occupy a shell is given by the formula , where is the principal quantum number representing the shell number.

K shell: n = 1, maximum electrons =
L shell: n = 2, maximum electrons =
M shell: n = 3, maximum electrons =
N shell: n = 4, maximum electrons =

Therefore, the maximum number of electrons in the M shell is 18.

The number of degenerate orbitals in a subshell is determined by the number of possible values for the magnetic quantum number, . For a given value of the azimuthal quantum number, , the magnetic quantum number can take on values from to , including 0.

That is, .

The total number of possible values (and thus degenerate orbitals) is . For a subshell, the azimuthal quantum number . Therefore, the number of degenerate orbitals is:

Therefore, the number of degenerate orbitals in a 4d subshell is 5.