alleryStart learning →A calcium atom loses both of its valence electrons. Its 18 remaining electrons match which noble gas?
ANeon (Ne)
BKrypton (Kr)
CHelium (He)
DArgon (Ar)
Answer & Solution
Correct answer: D. Argon (Ar)
1. A neutral calcium atom holds 20 electrons.
2. Losing the two valence electrons leaves 18 electrons behind.
3. The noble gas with 18 electrons is argon, so the ion is isoelectronic with argon.
4. Neon has only 10 electrons, so it does not match the count.
_Source: OpenStax Chemistry (CC BY 4.0), Chs 7 and 17, section 7.1 Ionic Bonding_
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