Explain why the electronegativity of Ga, In and Tl will not vary very much.

Explanation

`to` Ga, In and Tl have the electro negativity values 1.6, 1.7 and 1.8 respectively.
`to` In Ga, In and Tl the d-electrons `(d^(10))` in penultimate shell do not shield the outer most electrons from nuclear attraction effectively.
`to` The reason for the above fact is the shielding effect of various electrons in the orbitals follows the order .
`s gt p gt d gt f`
Hence the outer electrons are held more firmly by the nucleus. Because of this, atoms with d electrons in the penultimate shell `(d^(10))` are smaller in size. Ga, In and Tl has same number of penultimate shell electrons.
`to` So, Ga, In and Tl will not vary very much in their electronegativities.