If one wished to remove substantially all of all chloride ions from an aqueous solution, this could be done by the addition of an aqueous solution of

Options

A. gelatin
B. starch
C. `AgNO_3`
D. `Na_2SO_4`

Explanation

To solve the problem of removing substantially all chloride ions from an aqueous solution, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Problem**: We need to remove chloride ions (Cl⁻) from an aqueous solution. This can be achieved through a chemical reaction that precipitates the chloride ions.

2. **Identifying the Precipitating Agent**: The most common way to remove chloride ions from a solution is to react them with silver ions (Ag⁺). When silver ions react with chloride ions, they form silver chloride (AgCl), which is an insoluble precipitate.

3. **Writing the Reaction**: The chemical reaction can be represented as:
\[ \text{Ag}^+ (aq) + \text{Cl}^- (aq) \rightarrow \text{AgCl} (s) \]
Here, AgCl(s) is the solid precipitate that forms when silver ions react with chloride ions.

4. **Choosing the Correct Reagent**: From the options given (gelatin, starch, silver nitrate, sodium sulfate), we need to identify which one contains silver ions. The only option that provides silver ions is **silver nitrate (AgNO₃)**.

5. **Conclusion**: By adding an aqueous solution of silver nitrate to the solution containing chloride ions, we can effectively remove the chloride ions by precipitating them as silver chloride.

### Final Answer:
The correct answer is **silver nitrate**.

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