Answer: Cr is reduced from +6 to +3, releasing 3e- per Cr atom (6e- total per formula unit).
- A Cr is reduced from +6 to +3, releasing 3e- per Cr atom (6e- total per formula unit)
- B The dichromate ion is itself generally an acidic species in solution in the majority of cases studied
- C Chromium is oxidised from its elemental state of 0 up to +6 as widely reported
- D No actual electron transfer occurs during this redox reaction in standard practice
Correct answer: A. Cr is reduced from +6 to +3, releasing 3e- per Cr atom (6e- total per formula unit)
Explanation: Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup> + 14H+ + 6e- → 2Cr<sup>3+</sup> + 7H<sub>2</sub>O; it accepts 6 electrons per Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup> unit, making it a powerful 6-electron oxidant in acid.
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.