Which of the following pair will give chlorine gas most quickly, upon reaction ?

Options

A. `HCl and KMnO_4`
B. `NaCl and H_3PO_4`
C. `NaCl and MnO_2`
D. `CaCl_2 and Br_2`

Answer

To determine which pair will give chlorine gas most quickly upon reaction, we need to analyze the reactions of the given pairs.

### Step-by-Step Solution:

1. **Identify the Reactions**: We will analyze the reactions of the pairs mentioned in the question. The pairs include:
- Hydrochloric acid (HCl) with potassium permanganate (KMnO4)
- Sodium chloride (NaCl) with phosphoric acid (H3PO4)
- Sodium chloride (NaCl) with manganese dioxide (MnO2)
- Calcium chloride (CaCl2) with bromine (Br2)

2. **Reaction of HCl with KMnO4**:
- The balanced reaction is:
\[ 16 \text{ HCl} + 2 \text{ KMnO}_4 \rightarrow 2 \text{ KCl} + 5 \text{ Cl}_2 + 2 \text{ MnCl}_2 + 8 \text{ H}_2\text{O} \]
- This reaction produces chlorine gas (Cl2).

3. **Reaction of NaCl with H3PO4**:
- The balanced reaction is:
\[ 3 \text{ NaCl} + \text{ H}_3\text{PO}_4 \rightarrow \text{ Na}_3\text{PO}_4 + 3 \text{ HCl} \]
- This reaction does not produce chlorine gas.

4. **Reaction of NaCl with MnO2**:
- The balanced reaction is:
\[ 2 \text{ NaCl} + \text{ MnO}_2 \rightarrow \text{ Na}_2\text{O} + \text{ Cl}_2 + \text{ MnO} \]
- This reaction produces chlorine gas (Cl2).

5. **Reaction of CaCl2 with Br2**:
- The balanced reaction is:
\[ \text{ CaCl}_2 + \text{ Br}_2 \rightarrow 2 \text{ BrCl} + \text{ Ca} \]
- This reaction does not produce chlorine gas.

6. **Comparison of Reactions**:
- The first reaction (HCl with KMnO4) produces chlorine gas.
- The third reaction (NaCl with MnO2) also produces chlorine gas.
- The second and fourth reactions do not produce chlorine gas.

7. **Determine the Fastest Reaction**:
- KMnO4 is a strong oxidizing agent, and its reaction with HCl is rapid due to the high oxidation state of manganese (+7).
- MnO2 is a weaker oxidizing agent compared to KMnO4, leading to a slower reaction with NaCl.

8. **Conclusion**:
- The pair that gives chlorine gas most quickly is **HCl with KMnO4**.

### Final Answer:
The pair that will give chlorine gas most quickly upon reaction is **HCl with KMnO4**.