Which element has the electron configuration [Ar] 3d^10 4s^1?
Show the answer and explanation
Correct answer
A. Copper (Cu)
Principle or equation
The electron configuration of an element is determined by its atomic number. The configuration [Ar] 3d^10 4s^1 corresponds to a total of 18 (Ar) + 10 + 1 = 29 electrons, which is copper (atomic number 29).
Why this answer is correct
Argon (Ar) has 18 electrons. Adding 10 (3d) and 1 (4s) gives 29 electrons. Copper has atomic number 29, and its actual configuration is [Ar] 3d^10 4s^1 due to stability from a filled d subshell.
Example
For nickel (Z=28), the configuration would be [Ar] 3d^8 4s^2, not the given one.
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