The viscosity of a fluid depends on its temperature.

1. Liquids: The viscosity of liquids decreases with an increase in temperature. This is because the cohesive forces between liquid molecules weaken as the thermal energy increases, allowing them to flow more easily.
2. Gases: The viscosity of gases increases with an increase in temperature. This is because the random thermal motion of gas molecules increases, leading to more frequent collisions and momentum transfer between layers, which results in greater resistance to flow.

Therefore, the correct statement is that the viscosity of liquids decreases.