Balancing the redox equation in acidic medium

Steps:

• Write reduction half-equation: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O
• Write oxidation half-equation: Zn → Zn²⁺ + 2e⁻
• Multiply oxidation by 3 to balance electrons: 3Zn → 3Zn²⁺ + 6e⁻
• Combine half-equations: Cr₂O₇²⁻ + 3Zn + 14H⁺ → 2Cr³⁺ + 3Zn²⁺ + 7H₂O

Why C is correct:

• It satisfies charge balance (left: +3; right: +6, with 6e⁻ transfer) and atom conservation per redox stoichiometry.

Why the others are wrong:

• A: Omits Zn reactant and fails electron balance.
• B: Omits Zn reactant and mismatches Zn²⁺ coefficient.
• D: Incorrectly doubles dichromate, unbalancing Cr atoms and charge.

Final answer: C