What is screening effect ?

Explanation

Screening or shielding effect : Atoms having multielectron system, tlie outermost electrons do not feel much attraction towards nucleus. It is because of the presence of electrons between nucleus and outer electrons. So, outer electrons are screened or shielded from nucleus by inner electrons. This is known as screening or shielding effect.
Screening effect increases with the increase in number of inner shell electrons. Therefore, it becomes easy to remove an electron. Hence, ionization enthalpy decreases.