Which of the following statements is incorrect?

during oxidizing action in an acidic solution, ${Cr_2O_7}^{2-}$, gets converted to $Cr^{2+}$

The correct answer is Option (3) → during oxidizing action in an acidic solution, ${Cr_2O_7}^{2-}$, gets converted to $Cr^{2+}$

In acidic medium, the dichromate ion (Cr₂O₇²⁻) acts as a strong oxidizing agent and gets reduced according to the half-reaction:

Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O

So, it is converted to Cr³⁺ (green color), not Cr²⁺.

Cr²⁺ is a very strong reducing agent and is unstable in aqueous solution — it is not the product of dichromate oxidation.

Quick check of other statements (all correct):

1. Chromate ion (CrO₄²⁻) has tetrahedral geometry → Correct
2. Sodium and potassium dichromates are strong oxidizing agents → Correct
3. Potassium dichromate is used as a primary standard in volumetric analysis → Correct (because it is stable, pure, high molar mass, and does not absorb moisture)