Which of the following double salt does not exists?

Options

A. `(NH_(4))_(2)SO_(4)*CuSO_(4)*6H_(2)O`
B. `(NH_(4))_(2)SO_(4)*FeSO_(4)*6H_(2)O`
C. `(NH_(4))_(2)SO_(4)*ZnSO_(4)*6H_(2)O`
D. `(NH_(4))_(2)SO_(4)*NiSO_(4)*6H_(2)O`

Answer

To determine which of the given double salts does not exist, we will follow a systematic approach:

### Step 1: Understand the Concept of Double Salts
Double salts are defined as molecular compounds that consist of two different salts that crystallize together in a specific ratio. They retain their identity only in the solid state and dissociate into their constituent ions when dissolved in water.

### Step 2: Analyze the Given Options
We need to evaluate each option provided to identify which one does not exist as a double salt. The options are:
- A: (NH4)2SO4·ZnSO4·6H2O
- B: (NH4)2SO4·MgSO4·6H2O
- C: (NH4)2SO4·ZnSO4·6H2O
- D: (NH4)2SO4·FeSO4·6H2O

### Step 3: Check the Existence of Each Double Salt
1. **(NH4)2SO4·ZnSO4·6H2O**: This is a proposed double salt of ammonium sulfate and zinc sulfate. However, it is known that zinc sulfate does not form a stable double salt with ammonium sulfate.
2. **(NH4)2SO4·MgSO4·6H2O**: This double salt exists and is known as ammonium magnesium sulfate.
3. **(NH4)2SO4·FeSO4·6H2O**: This double salt also exists and is known as ammonium iron sulfate.
4. **(NH4)2SO4·ZnSO4·6H2O**: As previously mentioned, this does not exist as a stable double salt.

### Step 4: Conclusion
Based on the analysis, the double salt that does not exist is **C: (NH4)2SO4·ZnSO4·6H2O**.

### Final Answer
The double salt that does not exist is **C: (NH4)2SO4·ZnSO4·6H2O**.

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