How does atomic radius affect coulombic attraction?

The bigger the size of the atom, the electrons, especially the valence electrons are further away from the nucleus. The nucleus is not able to pull the electrons, that are in orbitals further away from the nucleus, towards itself and the coulombic attraction decreases.

Explanation:

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.