which of the following will have the highest coagulating power for `Fe(OH)_(3)` colloid ?

Options

A. `PO_(4)^(3-)`
B. `SO_(4)^(2-)`
C. `Ca^(2+)`
D. `Al^(3+)`

Answer

To determine which of the given options has the highest coagulating power for the `Fe(OH)_(3)` colloid, we need to analyze the charge of each species provided in the options and apply Hardy-Schulze's rule.

### Step-by-Step Solution:

1. **Identify the Charge of `Fe(OH)_(3)` Colloid**:
- Ferric hydroxide, `Fe(OH)_(3)`, is a positively charged colloid. This means that it will coagulate in the presence of negatively charged ions.

2. **List the Given Options**:
- Option 1: Phosphate anion (PO4^3-)
- Option 2: Sulfate anion (SO4^2-)
- Option 3: Calcium cation (Ca^2+)
- Option 4: Aluminum cation (Al^3+)

3. **Determine the Charge of Each Option**:
- Phosphate (PO4^3-) has a charge of -3.
- Sulfate (SO4^2-) has a charge of -2.
- Calcium (Ca^2+) has a charge of +2.
- Aluminum (Al^3+) has a charge of +3.

4. **Apply Hardy-Schulze's Rule**:
- According to Hardy-Schulze's rule, the coagulating power of an ion is directly proportional to the charge of the ion. The higher the charge, the greater the coagulating power.
- Since `Fe(OH)_(3)` is positively charged, we are interested in the negatively charged ions for coagulation.

5. **Compare the Charges of Negatively Charged Ions**:
- Phosphate (PO4^3-) has a charge of -3.
- Sulfate (SO4^2-) has a charge of -2.
- The other two options (Calcium and Aluminum) are positively charged and do not contribute to the coagulation of the positively charged `Fe(OH)_(3)`.

6. **Conclusion**:
- Since phosphate (PO4^3-) has the highest negative charge (-3) compared to sulfate (SO4^2-) (-2), it will have the highest coagulating power for `Fe(OH)_(3)` colloid.

### Final Answer:
**Phosphate anion (PO4^3-) will have the highest coagulating power for `Fe(OH)_(3)` colloid.**