According to Hardy`-` Schulze rule, the coagulating power of cation follows the order :

Options

A. `Na^(+)gtBa^(2+)gtAl^(3+)`
B. `Al^(3+)gtBa^(2+)gtNa^(+)`
C. `Ba^(2+)gtAl^(3+)gtNa^(+)`
D. `Al^(2+)gtNa^(+)gtBa^(2+)`

Explanation

To solve the question regarding the coagulating power of cations according to Hardy-Schulze rule, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Hardy-Schulze Rule**:
- The rule states that the coagulating power of a cation is directly proportional to the charge of the cation. This means that cations with higher charges will have greater coagulating power.

2. **Identify the Cations**:
- In this question, we need to consider the cations provided: Al³⁺ (Aluminum), Ba²⁺ (Barium), and Na⁺ (Sodium).

3. **Determine the Charges**:
- Al³⁺ has a charge of +3.
- Ba²⁺ has a charge of +2.
- Na⁺ has a charge of +1.

4. **Rank the Cations by Charge**:
- According to the charges, we can rank them:
- Al³⁺ (charge +3) - highest coagulating power
- Ba²⁺ (charge +2) - second highest coagulating power
- Na⁺ (charge +1) - lowest coagulating power

5. **Write the Order of Coagulating Power**:
- Therefore, the coagulating power of the cations follows the order:
- Al³⁺ > Ba²⁺ > Na⁺

6. **Select the Correct Option**:
- Based on the order derived, we can identify the correct option from the provided choices.

### Final Answer:
The coagulating power of cations follows the order: **Al³⁺ > Ba²⁺ > Na⁺**.