Which one of these substances is called a pseudosolid?

Options

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

Answer

To determine which substance is called a pseudosolid, we need to understand the definition and characteristics of a pseudosolid.

### Step-by-Step Solution:

1. **Definition of Pseudosolid**: A pseudosolid is a type of solid that exhibits properties similar to those of a liquid. This means that, under certain conditions, it can flow slowly like a liquid.

2. **Characteristics of Pseudosolids**: Pseudosolids are not rigid in the same way that typical solids are. They can deform over time when subjected to stress, similar to how liquids behave. An example of this behavior is seen in glass, which is often described as a "supercooled liquid."

3. **Example of Pseudosolid**: The most commonly cited example of a pseudosolid is glass. It has a structure that is solid but can flow very slowly over time, which is why the base of glass objects is often thicker than the top.

4. **Conclusion**: Based on the definition and characteristics of pseudosolids, the correct answer to the question is that glass is called a pseudosolid.

### Final Answer:
The substance that is called a pseudosolid is **Glass**.

---