Assertion :- There is considerable increase in covalent radius from N   to P. How ever from As to $Bi$   only a small increase in covalent radius is observed.
Reason:- Covalent and Ionic radii in a particular oxidation state increased down the group.

Covalent and ionic (in a particular state) radii increase in size down the group. There is a considerable increase in covalent radius from N to P. However, from As to Bi only a small increase in covalent radii(lanthanoid contraction) is observed. This is due to the presence of completely filled d and f-orbitals in heavier elements.