Answer:
Sodium, Magnesium, and Sulfer are all in the same period meaning they have the same number of electron shells.
Step-by-step explanation:
Periods are rows in the periodic table. The number of Valence electrons grows across the period (left to right) until reaching the electron shell's capacity.
Groups occur in columns in the periodic table and all have the same number of valence electrons, and the number of electron shells increase as you move downward on the table