Question

why iodine has large size than nitrogen ​

Answer 1

Explanation:

There are more electrons in the inner shells of a fluorine atom, so the outer electrons are shielded from the nuclear charge. Actually, iodine has a higher ionization energy than fluorine because it has a higher atomic number.

Answer 2

Iodine has much more electrons than nitrogen.
These electrons repel each other.
This causes size to increase
Other reason could be the more number of electrons are housed in different and bigger shells for iodine