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🧪 Chemistry  ·  d- and f-Block Elements  ·  NEET & JEE

The standard reduction potential E°(Mn3+/Mn2+) is unusually high (very positive) because:

Answer: Mn2+ (d5) has an extra-stable half-filled 3d subshell.

  • A Mn3+ already has a stable half-filled configuration
  • B Mn3+ is strongly hydrated
  • C Mn2+ (d5) has an extra-stable half-filled 3d subshell
  • D Mn2+ is a strong oxidising agent

Correct answer: C. Mn2+ (d5) has an extra-stable half-filled 3d subshell

Explanation: Mn2+ is d5 (half-filled, extra stable), so the reduction Mn3+ to Mn2+ is highly favourable, giving a large positive E°.

Colours of Common Transition Metal Ions (Aqueous)Cu²⁺ blueFe²⁺ pale greenFe³⁺ brown-yellowMn²⁺ pale pinkNi²⁺/Cr³⁺ greenColour arises from d-d electron transitions - d⁰ ions like Sc³⁺, Ti⁴⁺ are colourless

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.

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