Which of the following does not decrease with rise in temperature ?

Options

A. Density
B. Surface tension
C. Vapour pressure
D. Viscosity

Explanation

To solve the question "Which of the following does not decrease with rise in temperature?" we will analyze each option provided: density, surface tension, vapor pressure, and viscosity.

### Step-by-Step Solution:

1. **Understanding the Options**:
- We have four options: Density, Surface Tension, Vapor Pressure, and Viscosity. We need to determine which of these does not decrease when the temperature rises.

2. **Analyzing Density**:
- Density (D) is defined as mass (M) per unit volume (V). The relationship can be expressed as \( D = \frac{M}{V} \).
- As temperature increases, most substances expand, leading to an increase in volume. Since mass remains constant, an increase in volume results in a decrease in density.
- **Conclusion**: Density decreases with an increase in temperature.

3. **Analyzing Surface Tension**:
- Surface tension is the energy required to increase the surface area of a liquid due to intermolecular forces.
- Generally, as temperature increases, the kinetic energy of molecules increases, which reduces the intermolecular forces, leading to a decrease in surface tension.
- **Conclusion**: Surface tension decreases with an increase in temperature.

4. **Analyzing Viscosity**:
- Viscosity is a measure of a fluid's resistance to flow. It is affected by temperature; as temperature increases, the kinetic energy of the molecules increases, causing them to move more freely and reducing viscosity.
- **Conclusion**: Viscosity decreases with an increase in temperature.

5. **Analyzing Vapor Pressure**:
- Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid phase. It is directly proportional to temperature; as temperature increases, more molecules have enough energy to escape the liquid phase, increasing vapor pressure.
- **Conclusion**: Vapor pressure increases with an increase in temperature.

6. **Final Conclusion**:
- Among the options, only vapor pressure does not decrease with an increase in temperature; it actually increases. Therefore, the answer is **C. Vapor Pressure**.