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

Options

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

Explanation

To determine which statement about the sulfates of alkali metals is correct, we will analyze each statement provided in the question.

### Step 1: Analyze the first statement
**Statement 1:** "Except Li2SO4, all sulfates of other alkali metals are soluble in water."

- **Explanation:** Lithium sulfate (Li2SO4) is indeed less soluble in water compared to the sulfates of other alkali metals. While it is soluble, its solubility decreases with increasing temperature, which is an exception to the general trend observed in other alkali metal sulfates. Therefore, this statement is correct.

### Step 2: Analyze the second statement
**Statement 2:** "All sulfate salts of alkali metals except lithium sulfate form alum."

- **Explanation:** Alum is a type of double sulfate salt that typically forms from larger cations. Due to the small size of lithium, lithium sulfate does not form stable alums, while the sulfates of other alkali metals can form alums. Thus, this statement is also correct.

### Step 3: Analyze the third statement
**Statement 3:** "All sulfate salts of alkali metals except lithium sulfate do not decompose at high temperature."

- **Explanation:** Most alkali metal sulfates are stable and do not decompose at high temperatures. However, lithium sulfate behaves differently due to its unique properties. Thus, this statement is also correct.

### Conclusion
All three statements about the sulfates of alkali metals are correct. Therefore, the answer to the question is that all the given statements are correct.

### Final Answer
**Option 4: All of these statements are correct.**

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