Question

why electron gain enthalpy decrease down to groups

Answer 1

This is because, as we go down the group both the atomic size and nuclear charge increases, but the effect of atomic size is more prominent than that of nuclear charge. Hence, the force of attraction between the nucleus and the added electron decreases and thus enthalpy becomes less negative

Answer 2

I hope you help. !
This is because, as we go down thegroup both the atomic size and nuclear charge increases, but the effect of atomic size is more prominent than that of nuclear charge. Hence, the force of attraction between the nucleus and the added electrondecreases and thus enthalpy becomes less negative.