Question

If the Aufbau principle had not been followed, $Ca(Z=20)$ would have been placed in the?

• A. s-block
• B. p-block
• C. d-block
• D. f-block

Answer 1

The correct option is C d-block

Electronic configuration of Ca is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^2$.

Filling of 3d orbital starts after the filling of 4s orbitals. If the Aufbau principle had not been followed, the filling of 3d orbital would have been prior to filling of 4s orbital and the electronic configuration of Ca would have been $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^2$ and it would have been placed in the d-block. Hence, correct answer is C.