MCQ
Which has the highest value of ionic radius ?
- A${F^ - }$
- B$B^{3+}$
- ✓$O^{2-}$
- D$Li^+$
✓
Answer
Correct option: C.
$O^{2-}$
c
No. of electrons in $O ^{2-}=10$
No. of electrons in $O ^{2-}=10$
No. of electrons in $B ^{3+}=8$
No. of electrons in $Li ^{+}=4$
No. of electrons in $F ^{-}=10$
$F ^{-}$and $O ^{2-}$ have highest no. of electrons, thus the effective nuclear charge
$\{\left.\frac{\text { nuclear charge }}{\text { No. of electrons }}\right\}$ for them is less than $B$ and $Li$.
When effective nuclear charge increases, size of an ion decreases.
Amongst $F ^{-}$and $O ^{2-}$, size of $O ^{2-}$ is more than $F ^{-}$as size decreases on moving from left to right in a period.
Therefore, $O ^{2-}$ is largest in size.
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