JEE Main 201815 April

Exam: JEE Main
Year: 2018
Date: 15 April
Subject: Chemistry
Chapter: Classification of Elements and Periodicity in Properties

JEE Main 2018 · 15 April · Chemistry · Classification of Elements and Periodicity in Properties

For Na ^ + , Mg ^ 2 + , F ^ - and O ^ 2 - , the correct order of...

For

{Na}^{+}, {Mg}^{2 +}, {F}^{-}

and

{O}^{2 -}

, the correct order of increasing ionic radii is:

Options

A ${O}^{2 -} < {F}^{-} < {Na}^{+} < {Mg}^{2 +}$
B ${Na}^{+} < {Mg}^{2 +} < {F}^{-} < {O}^{2 -}$
C ${Mg}^{2 +} < {Na}^{+} < {F}^{-} < {O}^{2 -}$
D ${Mg}^{2 +} < {O}^{2 -} < {Na}^{+} < {F}^{-}$

Correct answer

C. ${Mg}^{2 +} < {Na}^{+} < {F}^{-} < {O}^{2 -}$

Step-by-step solution

Isoelectric series:

${Mg}^{2 +} < {Na}^{+} < {F}^{-} < {O}^{2 -}$

All have $10$ electrons. In the isoelectronic series, the proton/electron ratio decreases, so the size decrease because ${Z}_{eff}$ increases on decrease proton/electron ratio.

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