Question
The correct order of radii is
A.
$$N < Be < B$$
B.
$${F^ - } < {O^{2 - }} < {N^{3 - }}$$
C.
$$Na < Li < K$$
D.
$$F{e^{3 + }} < F{e^{2 + }} < F{e^{4 + }}$$
Answer :
$${F^ - } < {O^{2 - }} < {N^{3 - }}$$
Solution :
Effective nuclear charge (i,e. $$Z/e$$ ratio) decreases from
$${F^ - }$$ to $${N^{3 - }}$$ hence the radii follows the order :
$${F^ - } < {O^{2 - }} < {N^{3 - }}.\,Z/e\,\,{\text{for}}$$ $${F^ - } = \frac{9}{{10}} = 0.9,{\text{for}}\,\,{O^{2 - }} = \frac{8}{{10}} = .8,$$ $${\text{for}}\,\,{N^{3 - }} = \frac{7}{{10}} = 0.7$$