Multiple choice general knowledge math & puzzles How many electrons are found in the outermost shell of aluminum (Al, atomic number 13)? 2 3 5 8 Reveal answer Fill a bubble to check yourself B Correct answer Explanation Aluminum has an atomic number of 13. Its electron configuration is 2, 8, 3. The first shell holds 2, the second holds 8, and the third (outermost) shell holds the remaining 3 electrons, which determine its chemical valency.