which of the following is not a characteristic of a crystalline solid ? (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.

Options

A. Define and characterstic heat of fusion
B. Isotropic nature
C. A regular periodically repeated pattern of arrangement of consituent particles in the entire crystal
D. A true solid

Explanation

To determine which of the following is not a characteristic of a crystalline solid, let's analyze each option one by one.

1. **Definite and characteristic heat of fusion**:
- Crystalline solids have a specific melting point and a definite heat of fusion. This means that they absorb a specific amount of heat when they change from solid to liquid at their melting point.
- Therefore, this option is a characteristic of crystalline solids.

2. **Isotropic nature**:
- Isotropic materials have the same physical 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 option is **not** a characteristic of crystalline solids.

3. **A regular periodically repeated pattern of arrangement of constituent particles in the entire crystal**:
- Crystalline solids are defined by their orderly and repeating arrangement of particles (atoms, ions, or molecules). This regular structure is a fundamental characteristic of crystalline solids.
- Hence, this option is a characteristic of crystalline solids.

4. **A true solid**:
- Crystalline solids are indeed considered true solids, as they maintain a definite shape and volume.
- Thus, this option is also a characteristic of crystalline solids.

After analyzing all the options, we conclude that the correct answer is:

**(b) Isotropic nature** is not a characteristic of a crystalline solid.