Question

In Sodium atom, the screening of $3s$ electron is due to:

• A. $3s^2,3p^6$
• B. $4s^1$
• C. $1s^2,2s^2,2p^6$
• D. $3s^1$

Answer 1

The correct option is C $1s^2,2s^2,2p^6$

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. Valence electrons are attracted by nucleus and repelled by other electrons.
As Electronic Configuration of $Na$ atom is: $1s^{2}2s^{2}2p^{6}3s^1$
So, Intervening electrons between nucleus and valence electrons, that are responsible for screening effect are $1s^{2}2s^{2}2p^6$.