Question

The effective nuclear charge for $4s$ electrons of $Zn$ will be

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

Answer 1

The correct option is A 26.85

The electronic configuration of Zn is $\left[Ar\right]3d^{10},4s^2$
Net attractive force on the electron under consideration $=Z-S=\text{(Nuclear charge - screening effect)}$
Slater's Formula for screening constant

Each electron contributes 0.35 (total electrons minus 1) present in outermost shell.
In penultimate energy level, elecrons contribute 0.85.
A contribution of 1.0 is from remaining electrons (present in last but one energy level)

For $4s-$ electrons: $1\times 0.35+10\times 0.85+1.0\times 18=0.35+8.5+18.0=26.85$