Assertion (A): `Na_(2)S_(2)O_(3)` is a salt of unstable acid.
Reason (R) : `H_(2)S_(2)O_(3)` is a polyprotic acid.

Options

A. If both (A) and (R) are correc, 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) is incorrect, but (R) is correct.

Explanation

To solve the assertion and reasoning question, we will analyze each statement step by step.

### Step 1: Analyze the Assertion (A)
**Assertion (A):** `Na2S2O3` is a salt of an unstable acid.

- **Explanation:** Sodium thiosulfate (`Na2S2O3`) is indeed a salt formed from the reaction of a strong base (sodium hydroxide, `NaOH`) and a weak acid (thiosulfuric acid, `H2S2O3`). Thiosulfuric acid is known to be unstable and can decompose easily. Therefore, the assertion is **correct**.

### Step 2: Analyze the Reason (R)
**Reason (R):** `H2S2O3` is a polyprotic acid.

- **Explanation:** A polyprotic acid is defined as an acid that can donate more than one proton (H⁺ ion). Thiosulfuric acid (`H2S2O3`) can donate two protons, which qualifies it as a polyprotic acid. Thus, the reason is also **correct**.

### Step 3: Determine the Relationship Between A and R
- While both the assertion and the reason are correct, the reason does not provide a correct explanation for the assertion. The fact that `H2S2O3` is a polyprotic acid does not directly explain why `Na2S2O3` is a salt of an unstable acid.

### Conclusion
- Both A and R are correct, but R is not the correct explanation of A.

### Final Answer
- The correct option is: Both A and R are correct, but R is not the correct explanation of A.

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