Which one of the following(a or h) electronic configuration is more stable and why? (a) `3d^4 4s^2` (b) `3d^5 4s^2`

What may the possible oxidation state of transition metals with the following electronic configurations in the ground state of their atoms ? (i) 3d^(3)4s^(2) (ii) 3d^(5)4s^(2) (iii) 3d^(6)4s^(2) .

3 d^(10) 4 s^(0) electronic configuration exhibits

Q .Which of the following electron configurations is correct for nickel (atomic number "28" )? a) 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(1)3d^(9) (b) 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(2)3d^(8) (c) 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(0)3d^(10)

Which of the following elements shows 6s^(2) , 4f^(7) 5d^(1) electronic configuration ?

The element with electronic configuration 3d^(5)4s^(1) is