Complete the following chemical equations:
(i) `Na_2CrO_4+H_2SO_4to`
(ii) `MnO_2+KOH+O_2to`
(iii) `HgCl_2+SnCl_2 to`

Explanation

Let's complete the given chemical equations step by step.

### (i) Reaction of Sodium Chromate with Sulfuric Acid

**Step 1:** Identify the reactants and products.
- Reactants: Sodium Chromate (Na₂CrO₄) and Sulfuric Acid (H₂SO₄)
- Products: Sodium Dichromate (Na₂Cr₂O₇), Sodium Sulfate (Na₂SO₄), and Water (H₂O)

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