Which of the following is a double salt?

Options

A. Carnalite
B. Mohr's salt
C. Alum
D. All of the aovbe

Answer

To determine which of the given options is a double salt, we need to analyze each option based on their chemical formulas.

### Step 1: Identify the Compounds
The options provided are:
1. Carnallite
2. Mohr's salt
3. Alum
4. All of the above

### Step 2: Analyze Each Compound

**1. Carnallite (KCl·MgCl₂·6H₂O)**
- Carnallite is composed of potassium chloride (KCl) and magnesium chloride (MgCl₂), along with water of crystallization.
- Since it contains two different salts (KCl and MgCl₂), it qualifies as a double salt.

**2. Mohr's Salt (NH₄)₂Fe(SO₄)₂·6H₂O**
- Mohr's salt consists of ammonium sulfate and ferrous sulfate.
- It also contains two different salts, which makes it a double salt.

**3. Alum (General formula: M₂(SO₄)₃·24H₂O)**
- Alums are double sulfates of a monovalent metal (like K⁺ or Na⁺) and a trivalent metal (like Al³⁺ or Cr³⁺).
- Since it contains two different salts, it is also classified as a double salt.

### Step 3: Conclusion
All three compounds—carnallite, Mohr's salt, and alum—are double salts. Therefore, the correct answer is:

**Answer: All of the above**

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