Which of the followig ions will finally give a black precipitate with `Ag^(o+)` ion?

Options

A. `SO_3^(2-)`
B. `Br^(ɵ)`
C. `CrO_4^(2-)`
D. `S_2O_3^(2-)`

Explanation

To determine which ion will give a black precipitate with Ag^+ (silver ion), we need to analyze the possible reactions of the given ions with silver ions.

### Step-by-Step Solution:

1. **Identify the Possible Ions**:
We need to consider the ions that are typically tested in such questions. Common ions that can react with silver ions include sulfate (SO4^2-), bromide (Br^-), dichromate (Cr2O7^2-), and thiosulfate (S2O3^2-).

2. **Reactions with Silver Ion**:
- **Sulfate (SO4^2-)**: When sulfate reacts with silver ions, it forms silver sulfate (Ag2SO4), which is a white precipitate and does not turn black.
- **Bromide (Br^-)**: Silver bromide (AgBr) is formed when silver ions react with bromide ions. AgBr is a yellowish-white precipitate and does not turn black.
- **Dichromate (Cr2O7^2-)**: Silver dichromate (Ag2Cr2O7) is formed, which is an orange-red precipitate and does not turn black.
- **Thiosulfate (S2O3^2-)**: When thiosulfate reacts with silver ions, it forms silver thiosulfate (Ag2S2O3), which can further decompose in the presence of water to produce silver sulfide (Ag2S), which is a black precipitate.

3. **Conclusion**:
Among the ions listed, thiosulfate (S2O3^2-) is the only ion that will ultimately lead to the formation of a black precipitate when reacted with silver ions. The reaction can be summarized as follows:
- Ag^+ + S2O3^2- → Ag2S2O3 (white precipitate)
- Ag2S2O3 + H2O → H2SO4 + Ag2S (black precipitate)

Thus, the correct answer is thiosulfate (S2O3^2-).

### Final Answer:
The ion that will finally give a black precipitate with Ag^+ ion is **thiosulfate (S2O3^2-)**.