Answer: Half-filled d 5 is extra stable due to exchange energy and symmetry.
- A Half-filled d<sup>5</sup> is extra stable due to exchange energy and symmetry
- B The 3d subshell is usually filled largely before the 4s subshell
- C Chromium is a diamagnetic element with little unpaired electrons
- D The 4s subshell must usually retain exactly two electrons under most conditions encountered
Correct answer: A. Half-filled d<sup>5</sup> is extra stable due to exchange energy and symmetry
Explanation: A half-filled 3d<sup>5</sup> has all electrons unpaired with maximum exchange energy, giving it extra stability; one 4s electron 'migrates' to 3d.
Aqueous solutions of transition metal ions show characteristic colours caused by electrons absorbing visible light to jump between split d-orbitals; the exact colour depends on the metal, its oxidation state, and surrounding ligands.
Concept context
Transition metals (d-block) and lanthanides/actinides (f-block). Known for coloured compounds, variable oxidation states, complex formation, and catalytic properties. Frequently tested in JEE and NEET.