Question

Explanation of the presence of three unpaired electrons in nitrogen atom is given by:

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

Answer 1

The correct option is B Hund's rule

Hund's Rule of Maximum Multiplicity is an observational rule which states that a greater total spin state usually makes the resulting atom more stable. Accordingly, it can be taken that if two or more orbitals of equal energy are available, electrons will occupy them singly before filling them in pairs.
Nitrogen(N) has atomic no 7 and E.C = $1s^{2}2s^{2}2p^3$
Therefore in $2p$ subshell, pairing does not take place but all sub-orbitals are singly occupied by electrons as per the Hund's rule of maximum multiplicity.