Potassium dichromate on heating with conc. `H_2SO_4` and NaCl gives yellow coloured gas known as ........... which is used for the detection of ............. ions.

Explanation

To solve the question, we will break it down into steps:

### Step 1: Identify the Reactants
We have potassium dichromate (K₂Cr₂O₇), concentrated sulfuric acid (H₂SO₄), and sodium chloride (NaCl).

### Step 2: Understand the Reaction
When potassium dichromate is heated with concentrated sulfuric acid and sodium chloride, a chemical reaction occurs. The potassium dichromate reacts with the sulfuric acid and sodium chloride to produce chromyl chloride (CrO₂Cl₂), along with potassium chloride (KCl), water (H₂O), and sodium sulfate (Na₂SO₄).

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