Which of the following is not a characteristic of a crystalline solid ?

Options

A. Definite and characteristic heat of fusion
B. Isotropic nature
C. A regular periodically repeated pattern of arrangement of constituent particles in the entire crystal
D. A true solid

Explanation

To determine which of the following is not a characteristic of a crystalline solid, we will analyze the given statements one by one.

### Step-by-Step Solution:

1. **Understanding Crystalline Solids:**
- Crystalline solids are defined by their orderly and repeating arrangement of particles (atoms, ions, or molecules). This long-range order gives them distinct properties.

2. **Analyzing the First Statement:**
- **Statement:** "Definite and characteristic heat of fusion."
- **Analysis:** Crystalline solids have a specific heat of fusion because they have a uniform structure. When they melt, they do so at a specific temperature. This statement is **true**.

3. **Analyzing the Second Statement:**
- **Statement:** "Isotropic nature."
- **Analysis:** Crystalline solids are actually **anisotropic**, meaning their physical properties vary when measured in different directions. This statement is **false**.

4. **Analyzing the Third Statement:**
- **Statement:** "Irregular periodic repeated pattern of arrangement of constituent particles in the entire solid."
- **Analysis:** This statement describes an amorphous solid rather than a crystalline solid. Crystalline solids have a regular and repeating pattern. This statement is **false**.

5. **Analyzing the Fourth Statement:**
- **Statement:** "True solids."
- **Analysis:** Crystalline solids are indeed considered true solids due to their well-defined structure and properties. This statement is **true**.

### Conclusion:
The statement that is **not a characteristic of a crystalline solid** is the second statement regarding their isotropic nature, as crystalline solids are anisotropic.

### Final Answer:
The second statement, "Isotropic nature," is not a characteristic of a crystalline solid.

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