As we know that the electrons in an atom are arranged in subshells of the shells that are present around the nucleus of the atom in their increasing configuration number, viz. K shell is the inner most shell of any atom ans L,M,N and so on are the subsequent outer shells of the atom containing electron.
Among the subshells, s is having the electrons of the lowest energy of a particular shell and hence are the nearest to the nucleus of the atom.
From Coulomb's law we know that the force due to electrostatic charges in proximity is inversely proportional to the square of the distance between them and hence the nearest electron feels the most effect of the protons of the nucleus.
