Which of the following elements has a partially filled atomic orbital?

• A. Argon (Ar)
• B. Helium (He)
• C. Oxygen (O)
• D. Neon (Ne)

Answer: (C)

Verified step by step guidance

1. Understand what it means for an element to have a partially filled atomic orbital: this occurs when at least one of the orbitals in the outermost electron shell contains electrons but is not completely full according to the Pauli exclusion principle and Hund's rule.
2. Recall the electron configurations of the given elements: Helium (He), Neon (Ne), Argon (Ar), and Oxygen (O).
3. Write the electron configuration for each element using the Aufbau principle, which fills orbitals in order of increasing energy levels.
4. Identify which element has orbitals that are not fully filled in its outermost shell. For example, Oxygen has 6 valence electrons, so its outer p orbitals are partially filled.
5. Conclude that Oxygen (O) has partially filled atomic orbitals because its electron configuration ends with a partially filled p subshell, unlike the noble gases Helium, Neon, and Argon, which have completely filled outer shells.