UPSEE 2019 Solved Paper

Radii of anion is more than neutral element. Here, O−2 has 10e− and F has 10e− for isoelectronic species radius increases as

e−

p

ratio increases.
∵O−2

e

p

=

10

8

∴F−

e

p

=

10

9

So, radius order is O2−>F−.
On moving left to right in a period, effective nuclear charge increases as radius decreases. So, order of size is O2−>F−>O>F