Which of the following does not form double salts ?

Options

A. `Li_(2)SO_(4)`
B. `Na_(2)SO_(4)`
C. `K_(2)SO_(4)`
D. `Rb_(2)SO_(4)`

Explanation

To determine which of the following does not form double salts, we need to analyze the options provided in the question. Double salts are salts that contain more than one type of cation or anion. Let's evaluate each option step by step.

### Step-by-Step Solution:

1. **Understanding Double Salts**:
- Double salts are formed when two different salts crystallize together. They contain more than one type of cation or anion. A common example is potassium alum, which has the formula K₂SO₄·Al₂(SO₄)₃·24H₂O.

2. **Analyzing Each Option**:
- **Option A: Lithium Sulfate (Li₂SO₄)**:
- Lithium has a small ionic size, which makes it less likely to form double salts. Therefore, lithium sulfate does not typically form double salts.

- **Option B: Sodium Sulfate (Na₂SO₄)**:
- Sodium sulfate can form double salts, such as sodium aluminum sulfate (NaAl(SO₄)₂·12H₂O), which contains both sodium and aluminum cations.

- **Option C: Potassium Sulfate (K₂SO₄)**:
- Potassium sulfate can also form double salts, like potassium aluminum sulfate (K₂SO₄·Al₂(SO₄)₃·24H₂O), which contains potassium and aluminum cations.

- **Option D: Rubidium Sulfate (Rb₂SO₄)**:
- Rubidium sulfate can form double salts as well, similar to potassium and sodium sulfates. For example, it can form rubidium aluminum sulfate.

3. **Conclusion**:
- Among the given options, **Option A: Lithium Sulfate (Li₂SO₄)** does not form double salts due to the small size of the lithium ion, which prevents it from combining with other cations to form double salts.

### Final Answer:
**Lithium Sulfate (Li₂SO₄) does not form double salts.**

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