The equilibrium Cr₂ O₇²⁻ ⇌ 2 CrO₄²⁻ is shifted to the right in :

Solution

Chemistry ma’am · 4 steps

Balance the equation fully and you will see H⁺ on the right; remove it and the equilibrium moves right.

1. Complete the equation. The given equation hides water and H⁺. Balanced in full, dichromate reacts with water to give chromate and two H⁺ ions.

   Cr₂O₇²⁻ + H₂O ⇌ 2CrO₄²⁻ + 2H⁺

2. Apply Le Chatelier. In a basic medium, OH⁻ ions take up the H⁺ and form water. A product is being removed, so the equilibrium shifts right to replace it.
3. Other media. Adding acid adds H⁺, a product, so the equilibrium shifts left towards Cr₂O₇²⁻. A weakly acidic or neutral medium does not remove H⁺, so it gives no push to the right.
4. So. The shift to the right happens in a basic medium, option (b). You can see it in the lab: orange dichromate turns into yellow chromate.

The idea to keep. When an equation looks pH-independent, balance it with H₂O and H⁺ first. Then base removes H⁺ and acid adds it, and Le Chatelier tells you the direction.

Answer from the NTA final answer key. Solution by PrepWiser.