Question

Select the correct sequence of increasing radius (left to right):

• A. $S{e}^{2-},O^{2-},F^{-}$
• B. $C{a}^{2+},Ar,K^{+}$
• C. $Se,As,Ge$
• D. $Fe,F{e}^{2+},F{e}^{3+}$

Answer 1

The correct option is C $Se,As,Ge$

(A) $O^{2-}{F}^{-}$
$S{e}^{2-}$
(for isoelectronic anions,
size $\propto$ magnitude of negative charge)
$\to$ overall order $\to S{e}^{2-}>O^{2-}>F^{-}$
For isoelectronic cations
size $\propto \frac{1}{\text{magnitude of positive charge}}$
$\therefore Ar>K^{+}>C{a}^{2+}$