Question

Which from following rule / principle states that "No two electrons in an atom can have the same set of four quantum numbers"?

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

Hint:

Logic Tip: The word "Exclusion" is the key. It \textit{excludes} the possibility of two electrons being in the exact same quantum state. This is why a single orbital (which fixes $n, l,$ and $m_l$) can only hold two electrons, forcing them to have different spin quantum numbers ($m_s = +1/2$ and $-1/2$).

Answer 1

The Correct Option is A

Concept:
The fundamental rules for filling electrons in orbitals define atomic structure:

• Pauli's Exclusion Principle: No two electrons in an atom can have the same set of four quantum numbers ($n, l, m_l, m_s$). This means an orbital can hold a maximum of two electrons, and they must have opposite spins.
• Hund's Rule of Maximum Multiplicity: Electron pairing in degenerate orbitals (like p, d, f) will not take place until each orbital of that subshell is singly occupied with parallel spins.
• Aufbau Principle: Electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels.
• Heisenberg Uncertainty Principle: It is impossible to determine simultaneously both the exact position and momentum of an electron.

Step 1: Match the given statement to the corresponding principle.
The statement "No two electrons in an atom can have the same set of four quantum numbers" is the exact, verbatim definition of Pauli's exclusion principle. Therefore, option (A) is the correct answer.