Ferric hydroxide sol is positively charged colloid. The coagulating power of `NO_3^-, SO_4^(2-) and PO_4^(3-)` ions would be in the order

Options

A. `NO_3^(-) gt SO_4^(2-) gt PO_4^(3-)`
B. `SO_4^(2-) gt NO_3^(-) gt PO_4^(3-)`
C. `PO_4^(3-) gt SO_4^(2-) gt NO_3^-`
D. `NO_3^(-) = SO_4^(2-) =PO_4^(3-)`

Answer

To determine the coagulating power of the ions \( \text{NO}_3^- \), \( \text{SO}_4^{2-} \), and \( \text{PO}_4^{3-} \) on the positively charged colloid of ferric hydroxide, we can follow these steps:

### Step 1: Understand the Concept of Coagulation
Coagulation refers to the process where colloidal particles aggregate to form a precipitate. The coagulating power of an ion is influenced by its charge and valency. According to Hardy-Schulze rule, ions with higher valency have greater coagulating power.

### Step 2: Identify the Valency of Each Ion
- For \( \text{NO}_3^- \): The valency is 1 (it carries a single negative charge).
- For \( \text{SO}_4^{2-} \): The valency is 2 (it carries two negative charges).
- For \( \text{PO}_4^{3-} \): The valency is 3 (it carries three negative charges).

### Step 3: Compare the Coagulating Power Based on Valency
Since the coagulating power increases with the valency of the ions, we can rank the ions based on their valency:
- \( \text{PO}_4^{3-} \) has the highest valency (3), thus it has the highest coagulating power.
- \( \text{SO}_4^{2-} \) has the next highest valency (2), thus it has moderate coagulating power.
- \( \text{NO}_3^- \) has the lowest valency (1), thus it has the lowest coagulating power.

### Step 4: Write the Final Order of Coagulating Power
Based on the above analysis, the order of coagulating power from highest to lowest is:
\[ \text{PO}_4^{3-} > \text{SO}_4^{2-} > \text{NO}_3^- \]

### Conclusion
Thus, the coagulating power of \( \text{NO}_3^- \), \( \text{SO}_4^{2-} \), and \( \text{PO}_4^{3-} \) ions would be in the order:
\[ \text{PO}_4^{3-} > \text{SO}_4^{2-} > \text{NO}_3^- \]