Which property is shared by all elements in period 3 of the periodic table?

• A. They are all transition metals.
• B. They all have similar chemical reactivity.
• C. They all have the same number of electron shells.
• D. They all have the same number of valence electrons.

Answer: (C)

Verified step by step guidance

1. Identify what 'period 3' means in the context of the periodic table: Periods are the horizontal rows, so period 3 includes all elements in the third row.
2. Recall that elements in the same period have the same number of electron shells (energy levels) because each period corresponds to filling a new electron shell.
3. Understand that transition metals are found in the d-block (periods 4 and beyond), so elements in period 3 are not transition metals.
4. Recognize that elements in the same period do not necessarily have similar chemical reactivity because their valence electron configurations vary across the period.
5. Note that elements in the same period do not have the same number of valence electrons; valence electrons increase from left to right across a period.