Valence electrons determine chemical properties in periodic groups

Steps:

• Group 1 elements are alkali metals with one valence electron each.
• Chemical properties arise from how atoms interact via valence electrons.
• All Group 1 elements lose one electron to form +1 ions, leading to similar reactivity.
• Thus, identical outer-shell electrons explain their uniform behavior.

Why C is correct:

• Elements in the same group share chemical properties due to having the same number of valence electrons, as defined by the periodic table's group structure based on electron configuration.

Why the others are wrong:

• A: Metallic bonding affects physical properties like luster and ductility, not chemical reactivity.
• B: This repeats C's idea but includes redundant "their," making it less precise.
• D: Storage under oil prevents oxidation but results from, rather than causes, similar properties.

Final answer: C