Question

Which ion has the largest radius?

• A. $S{e}^{2-}$
• B. $F^{-}$
• C. $O^{2-}$
• D. $R{b}^{+}$

Answer 1

Answer: (A)

Being isoelectronic, greater the nuclear charge, smaller the size and lesser the nuclear charge, larger the size.
$\underset{(A.N.=8)}{O^{2-}}>\underset{(A.N.=9)}{F^{-}}$ ($10$ electrons)
$\underset{(A.N.=34)}{S{e}^{2-}}>\underset{(A.N.=37)}{R{b}^{+}}$ electrons)
$\therefore S{e}^{2-}$ has largest radius.