Q. Which of the following is correct order of increasing size?
A) $Br^{-} > S^{2 -} > Cl^{-} > Na^{+} > Mg^{2 +} > Be^{2 +}$
B) $Be^{2 +} > \ Mg^{2 +} > \ Na^{+} > S^{2 -} > Cl^{-} > Br^{-}$
C) $S^{2 -} > \ Cl^{-} > Br^{-} > Na^{+} > Mg^{2 +} > Be^{2 +}$
D) $Na^{+} > Mg^{2 +} > Be^{2 +} > Br^{-} > Cl^{-} > S^{2 -}$
Explanation
(a)
Ions $\ \ \ \ \ \ \ \ \ \ \ \ \ \ Be^{2 +}\ \ Cl^{-}\ \ S^{2 -}\ \ Na^{+}\ \ Mg^{2 +}\ \ Br^{-}$
Valence shell 1 3 3 2 2 4
Now, between $Na^{+}\ and\ Mg^{2 +},\ Na^{+} > Mg^{2 +}$ (isoelectronic), between $Cl^{-}\ and\ S^{2 -},\ S^{2 -} > Cl^{-}$ (isoelectronic) because for isoelectronic species size decreases as the atomic number increases. Hence, the order of increasing size is
$Be^{2 +} > \ Mg^{2 +} > \ Na^{+} > Cl^{-} > S^{2 -} > Br^{-}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.