`Na_(2)S_(2)O_(3)` is prepared by :

Options

A. reaching `H_(2)S_(2)O_(3)` with `NaOH`.
B. reacting `Na_(2)SO_(4)` with S is alkaline medium.
C. heating `NaOH` and S
D. reducing `Na_(2)SO_(4)` with S in acidic medium.

Explanation

To determine how `Na₂S₂O₃` (sodium thiosulfate) is prepared, we can analyze the given options step by step.

### Step 1: Analyze the first option
The first option suggests that `H₂S₂O₃` (thiosulfuric acid) reacts with `NaOH` (sodium hydroxide).

**Reaction:**
\[ H₂S₂O₃ + 2NaOH \rightarrow Na₂S₂O₃ + 2H₂O \]

**Products:**
This reaction produces `Na₂S₂O₃` and water.

**Conclusion:**
This method is valid for preparing `Na₂S₂O₃`.

### Step 2: Analyze the second option
The second option suggests that `sodium sulfate` reacts with sulfur.

**Reaction:**
\[ Na₂SO₄ + S \rightarrow Na₂S₂O₄ \]

**Products:**
This reaction yields `Na₂S₂O₄` (sodium dithionate), not `Na₂S₂O₃`.

**Conclusion:**
This method does not produce `Na₂S₂O₃`, so it is incorrect.

### Step 3: Analyze the third option
The third option states that `NaOH` is heated with sulfur.

**Reaction:**
\[ 6NaOH + 4S \rightarrow Na₂S₂O₃ + 2Na₂S + 2H₂O \]

**Products:**
This reaction produces `Na₂S₂O₃` along with sodium sulfide and water.

**Conclusion:**
This method is valid for preparing `Na₂S₂O₃`.

### Step 4: Analyze the fourth option
The fourth option is not provided in the transcript, but we can conclude based on the analysis of the first three options.

### Final Conclusion
From the analysis, the correct method to prepare `Na₂S₂O₃` is through the reaction of `NaOH` with sulfur, which is option C.

### Summary of Steps:
1. **First Option:** Valid method producing `Na₂S₂O₃`.
2. **Second Option:** Incorrect as it produces `Na₂S₂O₄`.
3. **Third Option:** Valid method producing `Na₂S₂O₃`.
4. **Conclusion:** The correct answer is the third option.