Which of the following electron configurations represents an atom of sulfur (atomic number 16) in an excited state?

• A. 1s^2 2s^2 2p^6 3s^2 3p^6
• B. 1s^2 2s^2 2p^6 3s^2 3p^3 4s^1
• C. 1s^2 2s^2 2p^6 3s^1 3p^5
• D. 1s^2 2s^2 2p^6 3s^2 3p^4

Answer: (C)

Verified step by step guidance

1. Step 1: Identify the ground-state electron configuration of sulfur (atomic number 16). Sulfur has 16 electrons, so fill the orbitals in order of increasing energy: 1s, 2s, 2p, 3s, and 3p until all 16 electrons are placed. The ground-state configuration is \$1\mathrm{s}^2 2\mathrm{s}^2 2\mathrm{p}^6 3\mathrm{s}^2 3\mathrm{p}^4$.
2. Step 2: Understand what an excited state means. An excited state occurs when one or more electrons have absorbed energy and moved to a higher energy orbital than in the ground state, without changing the total number of electrons.
3. Step 3: Examine each given electron configuration and check if it has 16 electrons total and if any electron is promoted to a higher energy orbital compared to the ground state.
4. Step 4: For example, the configuration \$1\mathrm{s}^2 2\mathrm{s}^2 2\mathrm{p}^6 3\mathrm{s}^1 3\mathrm{p}^5$ has 16 electrons but shows one electron moved from the 3s orbital to the 3p orbital, indicating an excited state.
5. Step 5: Confirm that the other configurations either represent the ground state or have incorrect electron counts or distributions, and thus are not excited states of sulfur.