Question

What is common between given cations and anions, $O^{2-},F^{-},N{a}^{+},M{g}^{2+},A{l}^{3+}$ ?

• A. All have same ionic radii.
• B. All are isoelectronic species having 10 electrons.
• C. All of them belong to the third period.
• D. The nature of oxides of all the ions is basic.

Answer 1

Answer: (B)

$O$ and $F$ are in period 2 while $Na,Mg$ and $Al$ are in period 3 .
Number of electrons in $O^{2-}=8+2=10,F^{-}=9+1=10,N{a}^{+}=11-1=$
$10,M{g}^{2+}=12-2=10,A{l}^{3+}=13-3=10$
Given ions have same number of electrons thus are isoelectronic species.
Thus the order of atomic radii is: $O^{2-}>F^{-}>N{a}^{+}>M{g}^{2+}>A{l}^{3+}$
All are isoelectronic species having 10 electrons.