Which of the following orbital-filling diagrams violates the Pauli exclusion principle?

• A. An orbital containing only one electron
• B. An empty orbital
• C. An orbital containing two electrons with parallel spins (both arrows pointing up)
• D. An orbital containing one electron with spin up and one with spin down

Answer: (C)

Verified step by step guidance

1. Recall the Pauli exclusion principle, which states that no two electrons in the same atom can have the same set of four quantum numbers. In terms of orbital diagrams, this means that an orbital can hold a maximum of two electrons, and these two electrons must have opposite spins.
2. Analyze the given options: an orbital with only one electron is allowed because it does not violate the spin rule; an empty orbital is obviously allowed since it contains no electrons.
3. Consider the option with two electrons having parallel spins (both arrows pointing up). This configuration violates the Pauli exclusion principle because both electrons would have the same spin quantum number, which is not allowed.
4. The option with one electron spin up and one electron spin down in the same orbital is allowed because the electrons have opposite spins, satisfying the Pauli exclusion principle.
5. Therefore, the orbital-filling diagram that violates the Pauli exclusion principle is the one with two electrons having parallel spins in the same orbital.