The increase in electro negativity when moving left to right on the periodic table can be explained by what?

Decrease in size

Explanation:

Electronegativity is defined as the property of an element to attract a shared pair of electron towards itself.

On moving across a period from left to right,   the size of an atom decreases because the electrons get added to the same shell and the nuclear charge keeps on increasing. Thus the electrons get more tightly held by the nucleus.

As, the size of an element decreases, the valence electrons come near to the nucleus. So, the attraction between the nucleus and the shared pair of electrons increases. Thus electronegativity increases.

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