Assertion (A): `Sn` reacts with `HCl` to produce `H_(2)` gas.
Reason (R ): `Sn` is a better reducing agent than `H_(2)` gas.

Options

A. If both `(A)` and `(R )` are correct and `(R )` is the correct explanation of `(A)`.
B. If both `(A)` and `(R )` are correct but `(R )` is not the correct explanation of `(A)`.
C. If `(A)` is correct but `(R )` is incorrect.
D. If `(A)` and `(R )` are incorrect.

Explanation

To solve the question regarding the assertion and reason provided, we will analyze both statements step by step.

### Step 1: Analyze the Assertion
The assertion states that "Sn reacts with HCl to produce H2 gas."

- **Chemical Reaction**: The reaction can be represented as:
\[ \text{Sn} + 2 \text{HCl} \rightarrow \text{SnCl}_2 + \text{H}_2 \]
- In this reaction, tin (Sn) displaces hydrogen from hydrochloric acid (HCl), resulting in the formation of tin(II) chloride (SnCl2) and hydrogen gas (H2).

**Conclusion for Step 1**: The assertion is correct because Sn does indeed react with HCl to produce H2 gas.

### Step 2: Analyze the Reason
The reason states that "Sn is a better reducing agent than H2 gas."

- **Reducing Agent**: A reducing agent is a substance that donates electrons in a chemical reaction and is oxidized in the process. To determine if Sn is a better reducing agent than H2, we need to compare their standard reduction potentials.
- The standard reduction potential for the half-reaction:
\[ \text{Sn}^{2+} + 2e^- \rightarrow \text{Sn} \quad (E^\circ = -0.14 \text{ V}) \]
- The standard reduction potential for the half-reaction:
\[ 2\text{H}^+ + 2e^- \rightarrow \text{H}_2 \quad (E^\circ = 0.00 \text{ V}) \]
- Since the reduction potential of Sn is more negative than that of H2, it indicates that Sn can reduce other species (like H+) more effectively than H2 can. Therefore, Sn is indeed a better reducing agent than H2.

**Conclusion for Step 2**: The reason is correct because Sn has a lower (more negative) reduction potential than H2, confirming that it is a better reducing agent.

### Final Conclusion
Both the assertion and the reason are correct, and the reason provides a correct explanation for the assertion.

### Answer
Both assertion (A) and reason (R) are correct, and R is the correct explanation of A.