When filling degenerate orbitals, electrons fill them singly first, with parallel spins is known as When filling degenerate orbitals, electrons fill them singly first, with parallel spins is known as:

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

Answer : The correct option is, (A) Hund's rule

Explanation :

Hund's rule : It states that the electrons are singly filled first in each orbital having same spin, then only pairing occurs.

Heisenberg  uncertainty principle : It is defined as the position and the momentum both can not be determined simultaneously.

Aufbau principle : It states that the atom or ion that present in the ground state, the lowest energy level will be filled first before occupying the higher levels.

Pauli Exclusion Principle : It states that no two electrons present in an atom or a molecule can have the same set of the four quantum numbers.

Hence, the correct option is, (A) Hund's rule