Calcium and magnesium belong to the group of the periodic table because both?

Analyze the question: The question asks why calcium (Ca) and magnesium (Mg) are placed in the same group of the periodic table. The key principle is that elements are grouped by a shared feature of their electronic structure.

Concept: Elements in the same group have the same number of valence (outermost shell) electrons. This gives them similar chemical properties. Group position is decided by electron configuration, not by general traits like being a metal.

Step-by-step solution:

1. Write the electronic configurations: • Magnesium (Z = 12): 2, 8, 2 • Calcium (Z = 20): 2, 8, 8, 2

2. Both have 2 valence electrons, so both belong to Group 2 (the alkaline earth metals).

3. Check each option: • A. are metals: True, but so are sodium, iron and copper, which are in different groups. This does not explain why they share a group. • B. form cations: True, but all metals form cations, so this is not specific to the group. • C. form colourless salts: Not a basis for grouping. Many metals in other groups also form colourless salts. • D. have same number of valence electrons: Correct. This is the real reason for placing them in the same group.

Answer: D.

Tip: Whenever a question asks why elements are in the same group, think same number of valence electrons. If it asks why they are in the same period, think same number of electron shells.