To determine which element gains three electrons to fill its outermost energy level, we need to look at the position of each element in the periodic table and their electron configurations.
-
Sulfur (S) - Atomic number 16. It has six electrons in its outermost energy level (period 3) and typically gains 2 electrons to achieve a stable octet.
-
Nitrogen (N) - Atomic number 7. It has five electrons in its outermost energy level (period 2) and typically gains 3 electrons to achieve a stable octet.
-
Calcium (Ca) - Atomic number 20. It has two electrons in its outermost energy level (period 4) and typically loses 2 electrons to achieve a stable octet.
-
Neon (Ne) - Atomic number 10. It already has a complete outermost energy level (8 electrons) and does not need to gain or lose electrons.
Based on this analysis, the correct answer is Nitrogen (N), as it gains three electrons to fill its outermost energy level.