The `As_2S_3` colloid will be most readily coagulated by

Options

A. `MgCl_2`
B. `AlCl_3`
C. `Na_2SO_4`
D. `Na_3PO_4`

Explanation

To solve the question regarding the coagulation of the `As_2S_3` colloid, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Nature of the Colloid**:
- `As_2S_3` is a negatively charged colloid. This means that it will be coagulated by positively charged ions.

2. **Understand Hardy-Schulze Rule**:
- According to the Hardy-Schulze rule, the coagulating power of an ion is directly proportional to its valency. Higher the valency of the ion, greater will be its coagulating power.

3. **List the Given Options**:
- The options typically include ions such as `Mg^2+`, `Al^3+`, and `Na^+`. We need to evaluate the valency of each:
- `Mg^2+` has a valency of +2.
- `Al^3+` has a valency of +3.
- `Na^+` has a valency of +1.

4. **Determine the Ion with the Highest Valency**:
- Among the ions listed, `Al^3+` has the highest valency of +3. This means it has the greatest coagulating power according to the Hardy-Schulze rule.

5. **Conclusion**:
- Since `As_2S_3` is a negatively charged colloid, it will be most readily coagulated by the positively charged ion with the highest valency, which is `Al^3+` from `AlCl_3`.

### Final Answer:
- The `As_2S_3` colloid will be most readily coagulated by **AlCl3**.