Elements in the same period of the periodic table have the same

Correct Answer: Number of electron shells

Explanation:

• A period in the periodic table is a horizontal row of elements.
• All elements in the same period have their outermost electrons in the same principal energy level (shell).
• For example: - Period 2 elements (Li, Be, B, C, N, O, F, Ne) all have electrons in two shells. - Period 3 elements (Na, Mg, Al, Si, etc.) all have electrons in three shells.
• Their atomic numbers increase across the period, and their chemical/physical properties vary, not remain the same.

Thus, elements in the same period share the same number of electron shells.