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 each option provided:

1. **Definite and characteristic heat of fusion**: Crystalline solids have a specific melting point and a definite heat of fusion. This means that when they melt, they do so at a specific temperature and have a defined amount of energy required for the phase change. This statement is true.

2. **Isotropic nature**: Isotropic materials have identical properties in all directions. However, crystalline solids are typically anisotropic, meaning their properties can vary depending on the direction in which they are measured. Therefore, this statement is false and is not a characteristic of crystalline solids.

3. **Regular periodic pattern of arrangement of constituent particles**: Crystalline solids are defined by their orderly and repeating arrangement of particles (atoms, ions, or molecules). This characteristic is true for crystalline solids.

4. **True solid**: Crystalline solids are often referred to as true solids because they have a fixed shape and structure due to their orderly arrangement of particles. This statement is also true.

Based on the analysis above, the option that is not a characteristic of a crystalline solid is:

**Answer: Isotropic nature (Option 2)**