The ionic species having largest size is

Options

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

Explanation

To determine the ionic species with the largest size among the given options, we can follow these steps:

### Step 1: Understand the Options
We have four options to consider:
1. Li-Aquus (Lithium in aqueous solution)
2. Li-Positive Aquus (Lithium ion in aqueous solution)
3. Na-Positive Aquus (Sodium ion in aqueous solution)
4. Rb-Positive Aquus (Rubidium ion in aqueous solution)

### Step 2: Analyze Ionic Sizes
Ionic size generally increases as we move down a group in the periodic table. This is because additional electron shells are added, making the ions larger.

- **Lithium (Li)**: Smallest ion among the options.
- **Sodium (Na)**: Larger than lithium.
- **Rubidium (Rb)**: Larger than sodium.

### Step 3: Consider Hydration Effects
In an aqueous solution, the size of the hydrated ion can differ from the ionic radius. Smaller ions tend to have a larger hydrated radius because they attract more water molecules around them.

- **Li+**: Although it is the smallest ion, it has a high charge density, which allows it to attract more water molecules, leading to a larger hydrated size.
- **Na+ and Rb+**: These ions are larger, but they attract fewer water molecules compared to Li+.

### Step 4: Compare Hydrated Sizes
Since we are interested in the hydrated sizes:
- Li+ will have a larger hydrated size compared to Na+ and Rb+ due to its smaller ionic radius and higher charge density.
- Therefore, in an aqueous medium, Li+ will have the largest effective size.

### Conclusion
The ionic species having the largest size in aqueous solution is **Li-Aquus**.

### Final Answer
**Li-Aquus** is the correct option.

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