Question

why the atomic radius of neon is larger than fluorine

Answer 1

The noble gases have completely filled valence orbitals. As all the orbitals are completely occupied by electrons and their octet is complete, they exist as monoatomic gases and do not form bonds with other atoms. Therefore, the inter-electronic repulsion is the maximum in noble gases as all the orbitals are fully filled. 

The atomic radius of neon is greater than that of fluorine because neon is monoatomic and therefore has non-bonded Van der Waal radii whose values are very large. Nobel gases have Van der Waal radii and not covalent radii (unlike other non metals of the same period) and Van der Waal radii are larger than covalent radii.

Answer 2

Because neon has more electrons than fluorine.we know each shall has limit to hold electron.As electrons increases it leads to more no.of shells
resulting in increased atomic radius.