Assertion :- `H_(2)` is the reducing agent and `Cl_(2)` is reduced in the reaction.
`H_(2)+Cl_(2)rarr2HCl`
Reason :- Reducing agent is the one which has been oxidised and decrease of oxidation number means reduction.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False.

Answer

To analyze the assertion and reason provided in the question, we can break it down into several steps:

### Step 1: Identify the Reaction
The reaction given is:
\[ H_2 + Cl_2 \rightarrow 2HCl \]

### Step 2: Determine Oxidation States
- In the reactants:
- The oxidation state of \( H_2 \) (hydrogen gas) is 0.
- The oxidation state of \( Cl_2 \) (chlorine gas) is also 0.

- In the products:
- In \( HCl \), the oxidation state of hydrogen (H) is +1.
- The oxidation state of chlorine (Cl) is -1.

### Step 3: Analyze Changes in Oxidation States
- For hydrogen:
- The oxidation state changes from 0 to +1, indicating that hydrogen is being oxidized (loss of electrons).

- For chlorine:
- The oxidation state changes from 0 to -1, indicating that chlorine is being reduced (gain of electrons).

### Step 4: Identify the Reducing and Oxidizing Agents
- A reducing agent is a substance that gets oxidized and causes another substance to be reduced.
- An oxidizing agent is a substance that gets reduced and causes another substance to be oxidized.

From the analysis:
- Hydrogen (\( H_2 \)) is the reducing agent because it is oxidized (its oxidation state increases).
- Chlorine (\( Cl_2 \)) is the oxidizing agent because it is reduced (its oxidation state decreases).

### Step 5: Evaluate the Assertion and Reason
- **Assertion**: "H2 is the reducing agent and Cl2 is reduced in the reaction."
- This is **true** as we have established that hydrogen is oxidized and chlorine is reduced.

- **Reason**: "Reducing agent is the one which has been oxidized and decrease of oxidation number means reduction."
- This is also **true**. The reducing agent (hydrogen) is oxidized, and the decrease in oxidation number (chlorine) indicates reduction.

### Conclusion
Both the assertion and reason are correct, and the reason correctly explains the assertion.

### Final Answer
Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.