Question

Why cr and mn called d block elements even their last electron filled in 4s?

Answer 1

Because their electronic configuration is different from the expected electronic configuration...since the half filled and the full filled orbitals are more stable due to large exchange of energy..

For,

Cr ..z=24

1s2 2s2 2p6 3s2 3p6 4s1 3d5 ( exception electronic configuration)

Now for,

Mn...z=25

1s2 2s2 2p6 3s2 3p6 4s2 3d5( exception)

Thus , it concludes that both cr and mn belongs to d-block elements since their last orbital is 'd'

Hope it helps you.....