Question
Question: The size of the following species increases in the order:...
The size of the following species increases in the order:

A
Mg2+ < Na+ < F−
B
F− < Na+ < Mg2+
C
Mg2+ < F− < Na+
D
Na+ < F− < Mg2+
Answer
(A) Mg2+ < Na+ < F−
Explanation
Solution
For isoelectronic species, size decreases as nuclear charge increases. F− (Z=9), Na+ (Z=11), Mg2+ (Z=12) all have 10 electrons. Therefore, Mg2+ < Na+ < F−.