Question

Which of the following electron arrangement does not obey Hund’s rule?

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

In Hund's rule, always remember that electrons fill degenerate orbitals singly before pairing up. This minimizes repulsion and stabilizes the atom.

Answer 1

The Correct Option is C

Hund's rule states that electrons will occupy degenerate orbitals (orbitals of the same energy level) singly before pairing up. In the given options: - Option (1) obeys Hund's rule: all three orbitals are fully paired, following the principle. - Option (2) also obeys Hund's rule: the two electrons in the first orbital are placed singly, then the second pair is formed. - Option (4) follows Hund's rule as well, as it places electrons singly in each orbital before pairing. However, option (3) does not obey Hund's rule because the second electron should have been placed singly in the available orbital rather than pairing up with the existing electron. According to Hund’s rule, the second electron should occupy a different orbital instead of pairing immediately. Thus, the correct answer is option (3).

Answer 2

The image shows three orbitals. The electrons are filled as:
1. First box: ↑↓ (two electrons with opposite spins)
2. Second box: ↑ (one electron)
3. Third box: empty

According to Hund’s Rule:
Electrons will occupy degenerate orbitals (orbitals with same energy) singly first, with parallel spins, before pairing begins.

In this configuration, pairing happens in the first orbital before the third orbital gets even a single electron, which violates Hund’s rule.

Correct Answer: The given electron arrangement in the image does not obey Hund’s rule.