How does the viscosity of a hydrocarbon change as its size increases?

The viscosity of a hydrocarbon is related to its molecular structure and the size of its molecules. As the size of a hydrocarbon increases, the length and complexity of its carbon chain also increase, leading to a greater number of intermolecular forces, particularly van der Waals forces.

Larger hydrocarbons have more extensive surface areas, which allows for stronger attractions between molecules. This results in a greater resistance to flow, meaning that larger hydrocarbons tend to have higher viscosity. Therefore, as hydrocarbons become larger and more complex, their viscosity increases, making the correct choice clear.

In contrast, smaller hydrocarbons tend to have lower viscosity due to weaker intermolecular forces and less surface area for interaction. The notion of viscosity remaining constant or fluctuating is less applicable in the context of hydrocarbons, as the general trend clearly shows that an increase in size correlates with an increase in viscosity.