How many moles of dichromate ion will be required to oxidize one mole of $Fe^{2+}$ to $Fe^{3+}$ ions in acidic solution?

1/6

The correct answer is Option (4) → 1/6

The half-reactions in acidic solution are:

Oxidation:

$Fe^{2+} → Fe^{3+} + e^-$

Reduction:

${Cr_2O}_7^{2-} + 14 H^+ + 6 e^- → 2 Cr^{3+} + 7 H_2O$

• 1 dichromate ion (Cr₂O₇²⁻) accepts 6 electrons.
• 1 Fe²⁺ loses 1 electron.

So, moles of dichromate needed per mole of Fe²⁺:

$\frac{1}{6}$