Complex forming tendency is more for-

Options

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

Answer

To determine which cation has the greatest complex forming tendency among the given alkali metal cations, we can follow these steps:

### Step 1: Identify the Cations
The cations in question are all alkali metal cations, which include:
- Li⁺ (Lithium)
- Na⁺ (Sodium)
- K⁺ (Potassium)
- Rb⁺ (Rubidium)

### Step 2: Understand Complex Forming Tendency
The complex forming tendency of a cation is influenced by its polarizing power. Polarizing power is the ability of a cation to distort the electron cloud of a nearby anion or ligand, leading to complex formation.

### Step 3: Relate Polarizing Power to Size and Charge
The polarizing power of a cation depends on two main factors:
1. **Size of the Cation**: Smaller cations have higher polarizing power.
2. **Charge of the Cation**: Greater charge increases polarizing power.

For alkali metal cations, they all have a +1 charge. Therefore, the size of the cation becomes the deciding factor for their polarizing power.

### Step 4: Compare the Sizes of the Cations
The order of cation sizes (from smallest to largest) is:
- Li⁺ < Na⁺ < K⁺ < Rb⁺

### Step 5: Determine the Cation with the Highest Polarizing Power
Since Li⁺ is the smallest cation among the given options, it will have the highest polarizing power and consequently the greatest complex forming tendency.

### Conclusion
Therefore, the cation with the greatest complex forming tendency is **Li⁺ (Lithium)**.

### Final Answer
The correct answer is **Li⁺ (Lithium)**.

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