Effective nuclear charge `(Z_(eff))` is the net attractive force on electrons under consideration and is equal to:
`Z_(eff) = Z - sigma` (nuclear charge - screening constant). `Z_(eff)` or `sigma` is calculated by Slater's formula, as given.
If one electrons is present in the outermst orbit, there will be no screening in that orbital. Each electrons contribute, `0.35` (total electrons minus one electron) present in the outermost shell.
A contribution of `0.85` for each electrons is taken in the `(n - 1)th` shell.
The screening constant `(sigma)` for `4s` electron of `Mn (Z = 25)` will be

Options

A. `18.00`
B. `4.25`
C. `18.35`
D. `22.6`

Answer

D

Explanation

Electronic configuration of `Mn(Z = 25)`.
`(1s^(2), 2s^(2)2p^(6), 3s^(2)3p^(6))/(("inner shell")), (3d^(5))/("(n-1)shell"), (4s^(2))/("nth shell")`
`(sigma)_(4s)^(1) = [["("0.35 xx "No. of electrons in the nth"],["shell"+"("0.85 xx "No. of electrons in"], ["(n-1)th shell)"+"("1.00 xx "Total no"],["of electrons in the inner shell "")"]]`
`= (0.35 xx 1) + (0.85 xx 5) + (1.00 xx 18)`
`=22.6`.