Question
What is the atomic number of an element having ns^1 electronic configuration and belonging to 3d transition series?
MHT CET
Chemistry
Structure of Atom
2026
MHT CET 2026 (13 April Shift 1)
MHT CET Chemistry Question (2026) — Solution
Options
- A. Only 24
- B. Only 25
- C. Only 29
- D. 24 and 29
Answer
D. 24 and 29
Step-by-step solution
The 3d transition series belongs to the 4th period, so n=4. The general electronic configuration of the 3d transition series is [Ar] 3d^ 1-10 4s^ 1-2 . Elements with an ns^1 (i.e., 4s^1) configuration in this series are Chromium (Cr) and Copper (Cu) due to the extra stability of half-filled and fully-filled d-subshells. The electronic configuration of Cr (Z=24) is [Ar] 3d^5 4s^1. The electronic configuration of Cu (Z=29) is [Ar] 3d^ 10 4s^1. Thus, the atomic numbers are 24 and 29. Answer: 24 and 29
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