Sodium, Magnesium, and Sulfer are all in the same period meaning they have the same number of electron shells.
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
The cells are identical because the DNA is copied during the S phase before cell division and then each resulting cell gets a matching copy of the chromosomes.
