Which of the following statement(s) is/are true?

Options

A. For gases, in general, viscosity increases with temperature
B. For liquids, viscosity varies directly with pressure
C. For gases, viscosity is independent of pressure
D. All of the above

Explanation

To determine which statements about viscosity are true, we will analyze the properties of viscosity in both gases and liquids based on the information provided in the video transcript.

### Step-by-Step Solution:

1. **Understanding Viscosity**:
- Viscosity is defined as the measure of a fluid's resistance to flow. It is quantified as the ratio of shear stress (force per unit area) to shear rate (velocity gradient).
- The coefficient of viscosity (η) is given by the formula:
\[ \eta = \frac{\text{Shear Stress}}{\text{Shear Rate}} \]

2. **Effect of Temperature on Viscosity**:
- For **liquids**, as the temperature increases, the viscosity typically **decreases**. This is because higher temperatures provide more energy to the molecules, allowing them to move more freely.
- For **gases**, the situation is different. As the temperature increases, the viscosity of gases generally **increases**. This is due to increased molecular activity and collisions among gas molecules.

3. **Effect of Pressure on Viscosity**:
- For **liquids**, viscosity varies **directly** with pressure. Increasing pressure can lead to an increase in viscosity as the molecules are forced closer together, making it harder for them to move past each other.
- For **gases**, viscosity is generally considered to be **independent** of pressure under normal conditions. The molecular interactions in gases are less affected by pressure changes compared to liquids.

4. **Evaluating the Statements**:
- **Statement A**: "For gases, in general, viscosity increases with temperature." - **True**
- **Statement B**: "For liquids, viscosity varies directly with pressure." - **True**
- **Statement C**: "For gases, viscosity is independent of pressure." - **True**
- **Statement D**: "All of the above." - **True** (since A, B, and C are true)

5. **Conclusion**:
- All the statements provided (A, B, C) are true, which means option D ("All of the above") is also true.

### Final Answer:
All of the statements A, B, and C are true, therefore option D is correct.

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