What is true about solids?

Options

A. They are known as fluids
B. Their constituent particles have no fixed position
C. Solids are rigid in nature
D. Their particles can move freely

Answer

To answer the question "What is true about solids?", we need to analyze the characteristics of solids based on the options provided.

### Step-by-Step Solution:

1. **Understanding Solids**:
- Solids are one of the three primary states of matter, along with liquids and gases. They have distinct properties that differentiate them from the other states.

2. **Analyzing the Options**:
- **Option 1**: "They are known as fluids."
- This statement is false. Solids are not fluids; fluids include liquids and gases, which can flow and take the shape of their container.

- **Option 2**: "Their constituents (particles) have no fixed position."
- This statement is also false. In solids, the particles (atoms, molecules, or ions) are packed closely together in a fixed arrangement and have a definite position.

- **Option 3**: "They have solid molecules and they have fixed position."
- This statement is true. Solids have a definite shape and volume due to the fixed positions of their particles.

- **Option 4**: "They are particles can move freely."
- This statement is false. In solids, particles can vibrate in place but cannot move freely as they do in liquids and gases.

3. **Conclusion**:
- The true statement about solids is: "They have solid molecules and they have fixed position."

### Final Answer:
The correct statement about solids is that they have solid molecules and they have a fixed position.

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