It is these attractive forces that are responsible for the viscosity since it is difficult for individual molecules to move because they are tightly bound to their neighbors. As the temperature is increased the thermal or kinetic energy of each molecule is increased and the molecules become more mobile. The attractive binding energy is lessened and therefore the viscosity is reduced. If we continue to heat the liquid the kinetic energy will exceed the binding energy and molecules will escape from the liquid and it can become a vapor. Liquids of very similar density can have widely varying viscosities.
Density is an almost static property of a liquid.
It does not change with temperature and in most cases the density of a liquid is similar to that of the solid form of the same substance over the whole liquid range, i.e. from melting point to boiling point. We are using a sponge and different liquids to see how much is absorbed by the sponge depending on the thickness of the liquid. No, there is no relationship between the viscosity of a liquid and how much will be adsorbed by a sponge. It will take longer for a more viscous liquid to be soaked up. For example, take two bowls of corn syrup.