What is screening effect? How is it related to IE ?

Explanation

The electrons present in the inner shells act as screens between the nucleus and the valence shell electrons. In order words, these electrons partially neutralise the force fo attraction fo the nucleus, over the valence electrons. This is called, 'shielding or screening effect'.
When the screening effect increase (No. of inner electron-shells increase), the IP decreases.
THe magnitude of screening effect `prop 1/(I.P)`.