Which of the following salt on heating with solid `K_(2)Cr_(2)O_(7)` and Conc. `H_(2)SO_(4)` , orange red vapours are evolved which turn NaOH solution yellow.

Options

A. `NaBr`
B. `NaCl`
C. `NaNO_(3)`
D. `NaI`

Explanation

To solve the question, let's break it down step by step:

### Step 1: Identify the Reaction
We need to determine which salt, when heated with solid potassium dichromate (K₂Cr₂O₇) and concentrated sulfuric acid (H₂SO₄), produces orange-red vapors. The orange-red vapors are typically associated with the formation of chromyl chloride (CrO₂Cl₂).

### Step 2: Analyze the Options
The options given are:
- A) NaPr (Sodium Propionate)
- B) NaCl (Sodium Chloride)
- C) NaNO₃ (Sodium Nitrate)
- D) NaI (Sodium Iodide)

Among these, we need to identify which salt contains chlorine, as chromyl chloride is derived from chlorine-containing compounds.

### Step 3: Identify the Salt with Chlorine
From the options:
- NaPr does not contain chlorine.
- NaCl contains chlorine.
- NaNO₃ does not contain chlorine.
- NaI contains iodine, not chlorine.

Thus, the only salt that contains chlorine is **NaCl**.

### Step 4: Write the Reaction
When NaCl is heated with K₂Cr₂O₇ and concentrated H₂SO₄, the following reaction occurs:

\[ 6 \, \text{NaCl} + 4 \, \text{K}_2\text{Cr}_2\text{O}_7 + 12 \, \text{H}_2\text{SO}_4 \rightarrow 4 \, \text{KHSO}_4 + 6 \, \text{NaHSO}_4 + 6 \, \text{H}_2\text{O} + 2 \, \text{CrO}_2\text{Cl}_2 \]

This reaction produces chromyl chloride (CrO₂Cl₂), which is responsible for the orange-red vapors.

### Step 5: Reaction with NaOH
The chromyl chloride (CrO₂Cl₂) reacts with sodium hydroxide (NaOH) to form sodium chromate (Na₂CrO₄), which is yellow in color:

\[ 2 \, \text{CrO}_2\text{Cl}_2 + 4 \, \text{NaOH} \rightarrow 2 \, \text{Na}_2\text{CrO}_4 + 2 \, \text{NaCl} + 2 \, \text{H}_2\text{O} \]

### Conclusion
Thus, the salt that, when heated with K₂Cr₂O₇ and concentrated H₂SO₄, produces orange-red vapors and turns NaOH solution yellow is **B) NaCl**.

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