The electronic configuration of valence shell of Cu is `3d^(10)4s^(2)`. How is this configuration explained ?

The electronic configuration of valence shell of Cu is 3d^(10)4s^(1) and not 3d^(9)4s^(2) . How is this configuration explained?

The electronic configuration of valence shell of Cu is 3d^(10)4s^(1) and not 3d^(9)4s^(2) . How is this configuration explained?

Electronic configuration in the valence shell of Barium is

The electronic configuration of Halogens in their valence shell is

The electronic configuration in the valence shell of silicon is The rule violated is

The electronic configuration of valence shell of Cr in the ground state as 3d^(5)4s^(1) in stead of 3d^(4)4s^(2) . Give reason.

The electronic configuration in the valence shell of silicon is . The rule violated is

Outer electronic configuration of Cu is ul(3d^9) ul (4s^2) .