Explain the term (a) screening effect

Explanation

### Step-by-Step Text Solution:

1. **Definition of Screening Effect**:
The screening effect, also known as the shielding effect, refers to the phenomenon where the nucleus of an atom exerts a reduced force of attraction on the valence electrons due to the presence of inner shell electrons.

2. **Mechanism of Screening Effect**:
The inner shell electrons create a barrier that "shields" the valence electrons from the full positive charge of the nucleus. This reduction in effective nuclear charge experienced by the valence electrons is what we call the screening effect.

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