J.C. Slater proposed an empirical constant that represents the cumulative extent to which the other electrons of an atom shield (or screen) any particular electron from the nuclear charge. Thus, slater's screening contant `sigma` is as : `Z^(**)=Z-sigma`
Here, Z is the atomic number of the atom, and hence is equal to the actual number of protons in the atom. the parameter `Z^(**)` is the effective nuclear charge, which according to is smaller than Z, since the electron in question is screened (shielded) from Z by an amount `sigma`. Conversely, an electron that is well shielded from the nuclear charge Z experiences a small effective nuclear charge `Z^(**)`.
The value of `sigma` for any one electron in a given electron configuration (i.e., in the presence of the other electrons of the atom in question) is calculated using a set of empirical rules developed by slater. according to these rules, the value of `sigma` for the electron in question is the cumulative total provided by the various other electrons of the atom.
Q. According to Slater's rule, order of effective nuclear charge `(Z^(**))` for last electron in case of Li, Na and K.

Options

A. `Li gt Na gt K`
B. `K gt Na gt Li`
C. `Na gt Li gt K`
D. `K=Na gt Li`

Answer

D

Explanation

`""_(3)Li implies 3 -(0.85xx2)implies 1.3`
`""_(11)Na implies 11-(0.85xx8+1xx2)=11-8.8=2.2`
`""_(19)K implies 19-(0.85xx8+1xx10)=19-16.8=2.2`