To solution of a salt in acid medium `AgNO_(3)` is added a white ppts repidly changing to yellow orange , brown and finaly black ppt is obtained .This isd due to the presence of

Options

A. `SO_(3)^(2-)`
B. `S_(2)O_(3)^(2-)`
C. `CH_(3)COO^(Theta)`
D. `S_(2)^(Theta)`

Answer

To solve the question regarding the observation of color changes when silver nitrate (AgNO₃) is added to a salt solution in an acidic medium, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reaction**: When silver nitrate (AgNO₃) is added to a solution containing thiosulphate ions (S₂O₃²⁻), a reaction occurs. The thiosulphate ions react with silver ions (Ag⁺) to form silver thiosulphate (Ag₂S₂O₃).

**Reaction**:
\[ 2 \text{AgNO}_3 + \text{Na}_2\text{S}_2\text{O}_3 \rightarrow 2 \text{Ag}_2\text{S}_2\text{O}_3 + 2 \text{NaNO}_3 \]

2. **Formation of Precipitate**: The silver thiosulphate formed is initially a white precipitate.

3. **Color Change Observations**: Over time, this white precipitate undergoes a series of color changes:
- **White**: Initial formation of silver thiosulphate.
- **Yellow**: The precipitate begins to change color as it ages.
- **Orange**: Further change in color occurs.
- **Brown**: The precipitate continues to darken.
- **Black**: Finally, the precipitate becomes black due to the formation of silver sulfide (Ag₂S).

4. **Final Reaction**: The black precipitate is attributed to the formation of silver sulfide (Ag₂S), which is a result of the decomposition of silver thiosulphate.

**Final Reaction**:
\[ 2 \text{Ag}_2\text{S}_2\text{O}_3 \rightarrow 2 \text{Ag}_2\text{S} + \text{S}_2\text{O}_3 \]

5. **Conclusion**: The presence of thiosulphate ions (S₂O₃²⁻) in the original salt solution is responsible for the observed color changes upon the addition of silver nitrate.

### Answer:
The color changes observed upon the addition of AgNO₃ are due to the presence of **thiosulphate ions (S₂O₃²⁻)**.

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