Question

Which of the following is not correct for electronic distribution in the ground state ?

Answer 1

check this pic please

Answer 2

The answer is (d) All of the above.

Following are some fundamental rules of chemistry that we should keep in mind before deciding the electronic configuration of an atom:

• Aufbau Principle: It suggests that the electrons should be filled in a subshell with lower energy first and then the subshell with higher energy can be filled.   The sequence of energy order is : 1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d<6p<7s<5f<6d<7p
• Pauli's Exclusion principle: This states that no two electrons shall have all four quantum numbers exactly the same. Therefore, it suggests that an orbital can accommodate a maximum of 2 electrons with opposite spin.
• Hund's Rule of Maximum Multiplicity: This suggests that in a subshell, the maximum number of unpaired electrons should be present in degenerate orbitals, and only then pairing takes place.

Applying the above rules to the following options we see that

1. Cobalt (Co) has the atomic number 27. In its ground state configuration, two electrons are present in the 4s orbital and 7 electrons are present in the 3d subshell. In the image only 4 electrons are present and that are also not in compliance with Hund's Rule.
2. Nickel (Ni) has the atomic number 28. In its ground state configuration, two electrons are present in the 4s subshell and 8 electrons are present in the 3d subshell. Here only 6 electrons are present in 3d and not in compliance with Hund's Rule.
3. Copper(Cu) has the atomic number 29. In its ground state, one electron is present in the 4s subshell and 10 electrons are present in 3d. This is an exception to Aufbau's Rule due to the extra stability of completely filled 3d subshell

Thus, we can see that all the configurations in the question are wrongly depicted.