The ions O ^ 2- , F ^ - , Na ^ + , Mg ^ 2+ and Al ^ 3+ are isoelectronic. Their ionic radii show :

NEET 2003 Chemistry question

The ions , , , and are isoelectronic. Their ionic radii show :

(1)A significant increase from to
(2)A significant decrease from to Correct
(3)An increase from to and then decrease from to
(4)A decrease from to and then increase from to

Answer: (2)

Solution

All five ions have 10 electrons, so the electronic shells are identical, but the nuclear charge increases from (O) to (Al). A larger nuclear charge pulls the same number of electrons closer, so the radius decreases steadily:

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Question ID VK-089185