Consider a titration of potassium dichromate solution with acidified Mohr's salt solution using diphenylamine as indicator.

Mohr’s salt is a mixture of ferrous sulfate and ammonium sulfate.

Mohr’s salt is FeSO₄ ( NH₄ )2SO₄

Potassium dichromate oxidizes ferrous sulfate.

Reaction occurs: .

K₂Cr₂O₄ + 6FeSO₄ + 7H₂SO₄ → K₂SO₄ + Cr₄2( SO₄ ) ₃ + 3Fe₄2( SO₄ ) ₃ + 7H₂O

6 moles of Ferrous sulphate reacts with 1 mole of potassium dichromate.

Thus, 6 moles of Mohr's salt are required for 1 mole of dichromate.

The option(D): 6 is correct.