Which of the following statement about the sulphate of alkali metal is correct ?

Options

A. Except `Li_(2)SO_(4)` all sulphate of other alkali metals are soluble in water
B. All sulphate salts of alkali metals except lithium sulphate forms alum
C. All sulphate salts of alkali metal except lithium sulphate do not decompose at high temperature.
D. All of these.

Explanation

To determine which statement about the sulphate of alkali metals is correct, we will analyze each statement based on our knowledge of the properties of alkali metal sulphates.

### Step-by-step Solution:

1. **Understanding Alkali Metal Sulphates**:
- Alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs).
- Sulphates are salts formed from sulphuric acid (H₂SO₄) and these metals.

2. **Solubility of Alkali Metal Sulphates**:
- It is known that all alkali metal sulphates, except lithium sulphate (Li₂SO₄), are soluble in water.
- Lithium sulphate has low solubility compared to the sulphates of other alkali metals.

3. **Formation of Alum**:
- Alums are double salts that typically have the formula K₂SO₄·Al₂(SO₄)₃·24H₂O or similar.
- It is true that all alkali metal sulphates, except lithium sulphate, can form alums. Hence, this statement is also correct.

4. **Thermal Stability of Sulphates**:
- The thermal stability of alkali metal sulphates increases as we move down the group.
- Lithium sulphate is less thermally stable compared to the sulphates of heavier alkali metals (like sodium, potassium, etc.). Therefore, this statement is also correct.

5. **Conclusion**:
- All the statements regarding the sulphates of alkali metals are correct:
- Except lithium sulphate, all sulphates of other alkali metals are soluble in water.
- All sulphate salts of alkali metals except lithium sulphate can form alum.
- All sulphates of alkali metals except lithium sulphate do not decompose at high temperatures.

### Final Answer:
All the statements regarding the sulphates of alkali metals are correct.

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