Which of the following is a psuedo solid ?

Options

A. `CaF_(2)`
B. Glass
C. NaCl
D. All

Explanation

To determine which of the following is a pseudo solid, we need to understand the definitions and characteristics of different types of solids.

### Step-by-Step Solution:

1. **Understand Types of Solids**:
- There are two main types of solids: crystalline solids and amorphous solids.
- Crystalline solids have a regular and ordered arrangement of particles. Examples include NaCl (sodium chloride) and CaF2 (calcium fluoride).
- Amorphous solids, on the other hand, lack a long-range order and have an irregular arrangement of particles.

2. **Definition of Pseudo Solid**:
- Amorphous solids are often referred to as pseudo-solids. The term "pseudo" means "false," indicating that they do not have the true solid structure of crystalline solids.
- Amorphous solids can also be described as "super-cooled liquids" because they can flow over time, albeit very slowly.

3. **Identifying the Pseudo Solid**:
- Given the options, we need to identify which one is an amorphous solid.
- Common examples of amorphous solids include glass, rubber, and some plastics.

4. **Conclusion**:
- Based on the definitions and characteristics discussed, the correct answer to the question "Which of the following is a pseudo solid?" is the option that represents an amorphous solid, which is typically glass.

### Final Answer:
- The pseudo solid among the options provided is **glass**.