The correct answer is option 'B': Viscosity of gas increases with an increase in temperature.

Viscosity is the measure of a fluid's resistance to flow. It is a property that determines the internal frictional resistance of a gas to flow when subjected to shear stress. The viscosity of a gas is influenced by various factors, including temperature and pressure.

Effect of Temperature on Viscosity:
When the temperature of a gas increases, the viscosity also increases. This is because as the temperature rises, the kinetic energy of the gas molecules also increases. The increased kinetic energy causes the gas molecules to move faster and collide with each other more frequently and with greater force. These collisions result in increased intermolecular interactions and stronger bonds between the gas molecules, leading to an increase in viscosity.

Explanation:
1. Gas Molecules and Kinetic Energy:
- Gas molecules are in constant random motion due to their kinetic energy.
- The kinetic energy of gas molecules is directly related to temperature. As temperature increases, the kinetic energy of the gas molecules also increases.
- This increased kinetic energy causes the gas molecules to move faster and collide more frequently.

2. Collisions and Intermolecular Interactions:
- When gas molecules collide, they exert forces on each other.
- These collision forces are responsible for the internal frictional resistance within the gas, which determines its viscosity.
- At higher temperatures, the increased kinetic energy of the gas molecules leads to more frequent and stronger collisions.
- These collisions result in increased intermolecular interactions and stronger bonds between the gas molecules.

3. Increased Viscosity:
- The increased intermolecular interactions and stronger bonds between gas molecules at higher temperatures result in an increase in viscosity.
- The gas molecules experience greater resistance to flow due to the increased intermolecular forces.
- This increased resistance leads to a higher viscosity of the gas.

Conclusion:
In summary, the correct option is 'B': Viscosity of gas increases with an increase in temperature. This is because the increased kinetic energy of gas molecules at higher temperatures leads to more frequent and stronger collisions, resulting in increased intermolecular interactions and higher viscosity.