Which pair is not isomorphous pair :-

Options

A. Green vitriol, Epsum salt
B. `KNO_(3), CaCO_(3)`
C. `NAF, Na_(2)O`
D. Potash alum, chrome alum

Answer

To determine which pair is not an isomorphous pair, we first need to understand the concept of isomorphism in chemistry.

### Step 1: Understand Isomorphism
Isomorphism refers to the phenomenon where two or more substances have the same crystal structure and similar atomic ratios of their constituent atoms. This means that the substances can crystallize in the same form, even if they are different compounds.

### Step 2: Analyze the Given Options
We have several pairs to evaluate:
1. Green vitriol (FeSO4·7H2O) and Epsom salt (MgSO4·7H2O)
2. KNO3 (Potassium nitrate) and CaCO3 (Calcium carbonate)
3. NAF (Sodium fluoride) and Na2O (Sodium oxide)
4. Potash alum (KAl(SO4)2·12H2O) and Chrome alum (CrAl(SO4)2·12H2O)

### Step 3: Evaluate Each Pair for Isomorphism
- **Green vitriol and Epsom salt**: Both have the same crystal structure (monoclinic) and similar atomic ratios, making them isomorphous.

- **KNO3 and CaCO3**: These two compounds have different crystal structures. KNO3 crystallizes in the orthorhombic system, while CaCO3 can crystallize in multiple forms (calcite, aragonite, etc.). Therefore, they are not isomorphous.

- **NAF and Na2O**: These compounds have different compositions and structures, thus they are not isomorphous.

- **Potash alum and Chrome alum**: Both have the same crystal structure and similar atomic ratios, making them isomorphous.

### Step 4: Conclusion
From the analysis, the pair that is not isomorphous is **KNO3 and CaCO3** due to their different crystal structures.

### Final Answer
The pair that is not isomorphous is **KNO3 and CaCO3**.

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