What is the lowest-energy electron configuration for zinc?

• A. A filled 3d energy level and a filled 4s energy level.
• B. A half-filled 3d energy level and a filled 4s energy level.
• C. A filled 3d energy level and a half-filled 4s energy level.
• D. A half-filled 3d energy level and a half-filled 4s energy level.

Answer: (A)

The lowest-energy electron configuration for zinc is characterized by a filled 3d subshell and a filled 4s subshell. Zinc has an atomic number of 30, which means it has 30 electrons. The electron configuration for zinc is written as [Ar] 4s² 3d¹⁰.

In terms of energy levels, the 4s subshell is filled with 2 electrons before the 3d subshell begins to fill. As the 3d subshell can hold a maximum of 10 electrons, zinc achieves a stable configuration with a fully filled 3d subshell. A filled 3d subshell contributes to greater stability and lower energy because it allows for maximum pairing of electrons with minimal repulsion.

In contrast, configurations that have either a half-filled, filled, or partially filled energy levels in 3d or 4s do not represent the most stable or low-energy state for zinc. In summary, the correct answer showcases zinc's stable electron configuration, with complete filling of both the 3d and 4s orbitals, minimizing electron-electron repulsion and maximizing stability.