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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Dinesh khalmaniya 1
1st oneis correct explanation- After the 4s is full we put the remaining six electrons in the 3d orbital and end with 3d9. Therefore the expected electron configuration for Copper will be 1s22s22p63s23p64s23d9. Note that when writing the electron configuration for an atom like Cu, the 3d is usually written before the 4s.