Question
What is the observed electronic configuration of Cu ?
MHT CET
Chemistry
Structure of Atom
2026
MHT CET 2026 (16 April Shift 1)
MHT CET Chemistry Question (2026) — Solution
Options
- A. [ Ar ]\ 3d^9\ 4s^2
- B. [ Ar ]\ 3d^ 10 \ 4s^1
- C. [ Ar ]\ 3d^5\ 4s^2
- D. [ Ar ]\ 3d^6\ 4s^2
Answer
B. [ Ar ]\ 3d^ 10 \ 4s^1
Step-by-step solution
The atomic number of copper (Cu) is 29. According to the Aufbau principle, the expected electronic configuration is [ Ar ]\ 3d^9\ 4s^2. However, a completely filled d-subshell (3d^ 10 ) provides extra stability due to symmetrical electron distribution and higher exchange energy. Therefore, one electron from the 4s orbital is transferred to the 3d orbital, resulting in the observed electronic configuration of [ Ar ]\ 3d^ 10 \ 4s^1. Answer: [ Ar ]\ 3d^ 10 \ 4s^1
Related: Chemistry — Structure of Atom · All PYQ Banks