Which of the following is true of both the sodium and chlorine atoms?

• A. Both have electrons arranged in three energy levels.
• B. Both have a full outermost electron shell.
• C. Both are noble gases.
• D. Both contain the same number of protons in their nuclei.

Answer: (A)

Verified step by step guidance

1. Identify the atomic numbers of sodium (Na) and chlorine (Cl). Sodium has an atomic number of 11, and chlorine has an atomic number of 17. This tells us the number of protons and electrons in each neutral atom.
2. Determine the electron configuration for each atom by filling electrons into energy levels (shells). Sodium (11 electrons) fills the first shell with 2 electrons, the second shell with 8 electrons, and the third shell with 1 electron. Chlorine (17 electrons) fills the first shell with 2 electrons, the second shell with 8 electrons, and the third shell with 7 electrons.
3. Analyze the number of energy levels occupied by electrons in both atoms. Both sodium and chlorine have electrons in three energy levels (shells), as seen from their electron configurations.
4. Evaluate the outermost electron shell for both atoms. Sodium has 1 electron in its outermost shell, so it is not full. Chlorine has 7 electrons in its outermost shell, which is also not full (full would be 8 electrons for these shells).
5. Check other options: Both are not noble gases (noble gases have full outer shells), and they do not have the same number of protons (11 vs. 17). Therefore, the true statement is that both have electrons arranged in three energy levels.