Magnesium cation has polarising power close to that of :

Options

A. `Li^(+)`
B. `Na^(+)`
C. `K^(+)`
D. `Cs^(+)`

Answer

To determine which cation has polarizing power close to that of the magnesium cation (Mg²⁺), we need to understand the concept of polarizing power and the relationship between the size and charge of cations.

### Step-by-Step Solution:

1. **Understanding Polarizing Power**:
- Polarizing power refers to the ability of a cation to distort the electron cloud of an anion. The greater the charge and the smaller the size of the cation, the higher its polarizing power.

2. **Identifying the Cation**:
- Magnesium cation is represented as Mg²⁺. It has a +2 charge and a relatively small ionic radius compared to other alkali and alkaline earth metals.

3. **Comparing with Other Cations**:
- We need to compare Mg²⁺ with the given options:
- a) Li⁺ (Lithium)
- b) Na⁺ (Sodium)
- c) K⁺ (Potassium)
- d) Cs⁺ (Cesium)

4. **Analyzing the Options**:
- **Li⁺**: Lithium has a +1 charge and a small ionic radius, which gives it significant polarizing power.
- **Na⁺**: Sodium has a +1 charge but a larger ionic radius than Li⁺, resulting in lower polarizing power than Li⁺.
- **K⁺**: Potassium also has a +1 charge and a larger ionic radius than Na⁺, leading to even lower polarizing power.
- **Cs⁺**: Cesium has the largest ionic radius among the options and a +1 charge, resulting in the lowest polarizing power.

5. **Conclusion**:
- Since Mg²⁺ has a +2 charge and a relatively small size, it is more similar in polarizing power to Li⁺ than to any of the other cations listed. Thus, the cation with polarizing power closest to that of Mg²⁺ is **Li⁺**.

### Final Answer:
The magnesium cation (Mg²⁺) has polarizing power close to that of **a) Li⁺ (Lithium)**.