Which pair is correctly matched ?

Options

A. `[Fe(OH)_(3)] Fe^(3+) :Cl^-`
B. `[As_(2)S_(3)] : As^(3+)`
C. `[SnO_(2)] : SnO_(3)^(2-)` in acidic medium
D. `[Agl] : I^(-)` in excess of `AgNO_(3)`

Answer

To determine which pair is correctly matched, we will analyze each option provided in the question step by step.

### Step 1: Analyze the first option
- **Statement**: Positive sol (Fe³⁺ ions) can be coagulated by anions.
- **Explanation**: A positive sol is one that has a net positive charge due to the presence of cations (like Fe³⁺). Coagulation occurs when oppositely charged ions (anions) are added, which neutralize the positive charge and cause the particles to aggregate. Therefore, this statement is correct.

### Step 2: Analyze the second option
- **Statement**: As₂S₃ preferentially adsorbs sulfide ions (S²⁻) to become a negative sol.
- **Explanation**: As₂S₃ does indeed preferentially adsorb sulfide ions, but the statement is misleading because it suggests that it adsorbs arsenic ions instead. The correct ion that would be adsorbed to create a negative sol is S²⁻, not As³⁺. Hence, this statement is incorrect.

### Step 3: Analyze the third option
- **Statement**: SnO₂ adsorbs SnO₃²⁻ in acidic medium.
- **Explanation**: This statement is incorrect because SnO₂ actually adsorbs SnO₃²⁻ in a basic medium, not in an acidic medium. The reaction occurs when a base is added to SnO₂, leading to the formation of a negatively charged sol. Therefore, this statement is incorrect.

### Step 4: Analyze the fourth option
- **Statement**: AgI in excess of AgNO₃.
- **Explanation**: When AgI is added to an excess of AgNO₃, it leads to the formation of a positive sol due to the presence of Ag⁺ ions. The statement incorrectly suggests that iodide ions are the adsorbed species, while in reality, it is the Ag⁺ ions that are present in excess. Therefore, this statement is also incorrect.

### Conclusion
After analyzing all the options, we find that the only correct match is the first option, which states that a positive sol (Fe³⁺ ions) can be coagulated by anions.

### Final Answer
The correct match is option **A**: Positive sol (Fe³⁺ ions) can be coagulated by anions.

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