Calculate the `Z_(eff)` at the periphery of the chromium atom.

Explanation

Imagine an extra electron in the outermost filled orbital(4s) of the chromium atom.
Electronic configuration of chromium ion (Cr= 24+1= 25) is `(1s^(2))(2s^(2)2p^(6))(3s^(2)3p^(6))(3d^(5))(4s^(2))`
The screening constant for the extra electron = `1xx 0.35 +(8+5) xx 0.85 +1.0 xx 10= 21.4`
Therefore,` Z_(eff)` at the periphery of the chromium atom = `Z-sigma= 24- 21.40 = 2.6`