Which of the following ions has the maximum polarising power?

Options

A. `Na^(+)`
B. `Ca^(2+)`
C. `Mg^(2+)`
D. `Al^(3+)`

Explanation

To determine which ion has the maximum polarizing power, we need to analyze the properties of the given ions: Na⁺, Mg²⁺, Al³⁺, and Ca²⁺.

### Step-by-Step Solution:

1. **Understand Polarizing Power**:
- Polarizing power refers to the ability of a cation to distort the electron cloud of an anion. It depends on two main factors: the charge of the cation and its size.
- The formula can be summarized as:
\[ \text{Polarizing Power} \propto \frac{\text{Charge}}{\text{Size}} \]

2. **Evaluate the Charge of Each Ion**:
- Na⁺ has a charge of +1.
- Mg²⁺ has a charge of +2.
- Al³⁺ has a charge of +3.
- Ca²⁺ has a charge of +2.
- From this, we can see that Al³⁺ has the highest charge.

3. **Consider the Size of Each Ion**:
- The ionic size generally decreases with increasing charge due to the greater effective nuclear charge pulling the electrons closer to the nucleus.
- Among the given ions, Al³⁺ is the smallest because it has the highest charge and is in the same period as Na⁺ and Mg²⁺, but with a higher positive charge.

4. **Comparing the Ions**:
- Na⁺ is larger than Mg²⁺, which is larger than Al³⁺.
- Ca²⁺ is larger than Mg²⁺ and Al³⁺ because it is in the next period down.

5. **Conclusion**:
- Since Al³⁺ has the highest charge and the smallest size, it will have the maximum polarizing power compared to the other ions.

### Final Answer:
The ion with the maximum polarizing power is **Al³⁺**.

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