Which one of the following is a redox reaction ?

Options

A. `H_(2)+Br_(2)rarr2HBr`
B. `2NaCl+H_(2)SO_(4)rarrNa_(2)SO_(4)+2HCl`
C. `HCl+AgNO_(3)rarrAgCl+HNO_(3)`
D. `NaOH+HClrarrNaCl+H_(2)O`

Answer

To determine which of the given reactions is a redox reaction, we need to analyze the oxidation states of the elements involved in each reaction. A redox reaction involves the transfer of electrons, where one species is oxidized (loses electrons) and another is reduced (gains electrons).

Let's go through the steps systematically:

### Step 1: Identify the reactions
We have several reactions to analyze. The first step is to list them out clearly.

1. Reaction involving H2 and Br2 to form HBr.
2. Reaction involving Na and Cl to form NaCl.
3. Reaction involving HCl and Na3.
4. Reaction involving NaH and Cl.

### Step 2: Determine oxidation states for each reaction
We will analyze the oxidation states of the elements in each reaction.

#### Reaction 1: H2 + Br2 → 2HBr
- **H2**: Each H has an oxidation state of 0 (elemental form).
- **Br2**: Each Br has an oxidation state of 0 (elemental form).
- **HBr**: H has an oxidation state of +1, and Br has an oxidation state of -1.

**Change in oxidation states**:
- H: 0 → +1 (oxidized)
- Br: 0 → -1 (reduced)

This indicates a redox reaction.

#### Reaction 2: Na + Cl → NaCl
- **Na**: Oxidation state of +1 in NaCl.
- **Cl**: Oxidation state of -1 in NaCl.

**Change in oxidation states**:
- Na: 0 → +1 (oxidized)
- Cl: 0 → -1 (reduced)

This indicates a redox reaction.

#### Reaction 3: HCl and Na3
- **H**: +1 in HCl.
- **Cl**: -1 in HCl.

No change in oxidation states occurs here, indicating this is not a redox reaction.

#### Reaction 4: NaH and Cl
- **Na**: +1 in NaH.
- **Cl**: -1 in NaH.

Again, no change in oxidation states occurs here, indicating this is not a redox reaction.

### Step 3: Conclusion
From the analysis, we find that:
- The first reaction (H2 + Br2 → 2HBr) is a redox reaction.
- The second reaction (Na + Cl → NaCl) is also a redox reaction.
- The third and fourth reactions do not involve changes in oxidation states and are not redox reactions.

### Final Answer
The first reaction (H2 + Br2 → 2HBr) is a redox reaction.