The correct order of increasing polarising power of the cations in the following `AlCl_(3) , MgCl_(3) , NaCl` is

Options

A. `AlCl_(3) lt MgCl_(3) lt NaCl`
B. `MgCl_(2) lt NaCl lt AlCl_(3)`
C. `NaCl lt MgCl_(2) lt AlCl_(3)`
D. `NaCl lt AlCl_(3) lt MgCl_(2)`

Explanation

To determine the correct order of increasing polarizing power of the cations in `AlCl_(3)`, `MgCl_(2)`, and `NaCl`, we need to analyze the cations present in each compound and their respective charges.

### Step-by-Step Solution:

1. **Identify the Cations**:
- In `AlCl_(3)`, the cation is `Al^(3+)`.
- In `MgCl_(2)`, the cation is `Mg^(2+)`.
- In `NaCl`, the cation is `Na^(+)`.

2. **Understand Polarizing Power**:
- The polarizing power of a cation refers to its ability to distort the electron cloud of an anion.
- It is influenced by the charge of the cation and its size. Generally, a higher charge and smaller size increase polarizing power.

3. **Compare the Charges**:
- `Na^(+)` has a charge of +1.
- `Mg^(2+)` has a charge of +2.
- `Al^(3+)` has a charge of +3.
- As the charge increases, the polarizing power also increases.

4. **Order the Cations by Polarizing Power**:
- Since `Na^(+)` has the lowest charge, it has the lowest polarizing power.
- `Mg^(2+)` has a higher charge than `Na^(+)`, so it has a higher polarizing power.
- `Al^(3+)` has the highest charge, thus it has the highest polarizing power.

5. **Final Order**:
- The order of increasing polarizing power of the cations is:
- `Na^(+)` < `Mg^(2+)` < `Al^(3+)`.

### Conclusion:
The correct order of increasing polarizing power of the cations in the compounds `AlCl_(3)`, `MgCl_(2)`, and `NaCl` is:
**Na^(+) < Mg^(2+) < Al^(3+)**.