Which of the following forms a criterion of purity of organic compound ?

Options

A. Molecular mass
B. Empirical mass
C. Melting or boiling point
D. Solubility.

Answer

To determine the criterion of purity for an organic compound, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Purity**: The purity of an organic compound refers to the extent to which it is free from impurities. Impurities can affect the physical properties of the compound.

2. **Identifying Criteria**: We need to identify which of the given options can serve as a reliable criterion for assessing the purity of an organic compound.

3. **Analyzing the Options**:
- **Option 1: Molecular Mass**: While molecular mass is a characteristic of a compound, it does not directly indicate purity. Different compounds can have the same molecular mass.
- **Option 2: Empirical Mass**: Similar to molecular mass, empirical mass does not provide information about the presence of impurities.
- **Option 3: Melting Point or Boiling Point**: The melting point and boiling point are significant physical properties that can indicate purity. Pure substances have sharp melting and boiling points, while impurities typically cause these points to broaden or shift.
- **Option 4: Solubility**: Solubility can vary with temperature and does not provide a definitive measure of purity.

4. **Conclusion**: Based on the analysis, the most reliable criterion for determining the purity of an organic compound is its melting point or boiling point. Therefore, the correct answer is **Option 3: Melting Point or Boiling Point**.

### Final Answer:
The criterion of purity of an organic compound is best indicated by its **melting point or boiling point** (Option 3).

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