Question

The presence of unpaired electron in phosphorous atom is explained by which principle?

• A. Aufbau principle
• B. Pauli's exclusion principle
• C. Hund's rule
• D. Heisenberg's principle

Hint:

Hund's Rule = Maximum multiplicity (keep electrons unpaired as long as possible).

Answer 1

The Correct Option is C

Step 1: Concept
Hund's rule states that pairing of electrons in orbitals of the same subshell does not occur until each orbital is singly occupied.
Step 2: Analysis
Phosphorous ($Z=15$) has the configuration $1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p_{x}^{1} 3p_{y}^{1} 3p_{z}^{1}$.
Step 3: Conclusion
The three electrons in the $3p$ subshell remain unpaired in separate orbitals according to Hund's rule.
Final Answer: (C)