Question

Why is the size of noble gas elements greater than halogens?

Answer 1

since all the electrons are paired and they cause inter electronic repulsions which weakens the effective nuclear force so electrons tend to move farther away from the nucleus cause of repulsions therefore radius is greater as well as size is always grater

Answer 2

Every entity in this world wish to be in stable state.
Noble gases are stable ,they neither need to loose electrons nor gan electrons whereas halogens need one electron to become stable ...So the size of noble gas element is greater than halogens
Hope it helps u !!