The electronic configuration of chromium, atomic number 24, is
Correct answer: C. [Ar] 3d5 4s1
- A. [Ar] 3d4 4s2
- B. [Ar] 3d6
- C. [Ar] 3d5 4s1
- D. [Ar] 4s2 4p4
Explanation
One 4s electron is promoted so that both the 3d and 4s subshells are exactly half filled, an arrangement of extra stability arising from symmetry and reduced electron repulsion. Copper behaves in the same way, adopting 3d10 4s1 to complete the d subshell. Writing 3d4 4s2 by mechanically following the filling order is the expected error.
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About Electronic Structure of d-Block Elements
The electronic structure of d-block elements covers the filling of the (n-1)d and ns orbitals, general electronic configurations, and the exceptions shown by chromium and copper. It explains how partially filled d orbitals produce variable oxidation states, coloured ions, magnetic behaviour and complex formation, while distinguishing transition elements from elements with completely filled d subshells.
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