Question

Why down a group electronegativity should increase with increase in nuclear charge but it is seen that electro negativity decreases

Answer 1

its true that down the group nuclear charge increases but down the group electron are added in a new shell which has higher principle quantum number like sodium has outermost configuration 3s1 and potassium has 4s1. so the size of atom increases. that's why the distance of outermost electron from nucleus decreases down the group. so attraction decreases down the group so electro negativity decreases.