Which of the following items has the lowest viscosity?

Kerosene has the lowest viscosity among the given options. Viscosity refers to a fluid's resistance to flow; therefore, the lower the viscosity, the more easily a fluid flows. Kerosene is a light hydrocarbon liquid used as fuel, generally with a lower molecular weight compared to the other oils listed. This lower molecular weight contributes to its fluidity and less resistance to flow, making it less viscous than heavier oils like #10 and #40 oil.

In contrast, cup grease, while also being fluid, has a higher resistance to flow than kerosene because it is designed to have a thicker consistency for lubrication purposes. The heavier oils, such as #10 and #40, possess greater viscosity because they are more dense and have a higher molecular weight, leading to even slower flow rates. The difference in viscosity between kerosene and these other substances is significant, as kerosene is used in applications where a low viscosity is advantageous.