Screening effect is the effect produced by intervening electrons between nucleus and valence electrons . They shield the nucleus from valence electron and effective nuclear charge decreases if there is less shielding effect the effective nuclear charge decreases Valence electrons are attracted by nucleus and repelled by other electrons. Net effective force on electrons under consideration =`Z-sigma`= (Nuclear charge -screening effect ) slaters formula for screening constant.
If one electron is present in outermost orbit there will be no screening in that orbital.
Each electrons contributes 0.35 (total electrons minus 1) present in outermost shell.
In penultimate energy level electrons contribute 0.85. A contribution of 1 is from remaining electrons (present in last but one energy level)
The effective nuclear charge for 4s electrons of Zn will be

Options

A. 26.85
B. 4.35
C. 15.3
D. 10

Answer

C