Chemistrymedium · Past Paper
The electronic configuration of an ion X2+ is 2, 8. What is the atomic number of X?
A8
B10
C12
D14
✓ Correct Answer: C — 12
X2+ means the atom lost 2 electrons. 10 (remaining) + 2 (lost) = 12 protons, so the atomic number is 12 (Magnesium).
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