Answer :
Answer: The correct sequence of filling electrons is option b. 4s comes before 3d.
Explanation:
The sequence of filling electrons in a neutral transition metal atom follows the Aufbau principle, which states that electrons fill the lowest energy orbitals first before moving to higher energy orbitals. The order of filling is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.
For a Period 4 neutral transition metal atom, the sequence of filling electrons would be 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p. This means that the 4s orbital is filled before the 3d orbital, making option b the correct answer.
It is important to note that while the 4s orbital is filled before the 3d orbital, the 3d orbital has a lower energy level and is therefore written before the 4s orbital in electron configurations.
For example, the electron configuration for a neutral chromium atom (atomic number 24) is [Ar] 3d^5 4s^1, even though the 4s orbital is filled before the 3d orbital.
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