Electronic configuration of `M^(3+)` is `[Ar]3d^(10)4s^(2)`, it belongs to

The electronic configuration of an elements is [Ar]3d^8 4S^2 . Name the block to which it belongs?

(A) : The electronic configuration of Cr is [Ar]3d^(5)4s^(1) but not [Ar]3d^(4)4s^(2) (R) : Lowering energy with configuration [Ar]3d^(5) 4s^(1) is more than that with configuration [Ar]3d^(4)4s^(2)

(A) : The electronic configuration of Cr is [Ar]3d^(5) 4s^(1) but not [Ar]3d^(4) 4s^(2) (R) : Lowering energy with configuration [Ar]3d^(5)4s^(1) is more than that with configuration [A]3d^(4)4s^(2)

Element with electronic configuration as [Ar]^(18)3d^(5)4s^(2) is placed in :

Element with electronic configuration as [Ar]^(18)3d^(5)4s^(2) is placed in :

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

Electronic configuration of copper is 3d^(10)4s^(1) instead of 3d^(9) 4s^(1) .Why?