Answer
Please see the work below.
Work Step by Step
The hindrance of nuclear attraction to the valence shell electrons by the inner core electrons is called the shielding effect.
The electronic configuration of Lithium is $1s^{2}2s^{1}$. Here the valence shell electron is the 2s electron and it is shielded by the two electrons present in 1s orbital. Therefore, the 2s electron does not experience the complete nuclear attraction.
