Pressure Effects on Viscosity

Viscosity is a measure of a fluid's resistance to deformation or flow. Pressure significantly influences the viscosity of both liquids and gases, particularly under extreme conditions.

Liquid Viscosity vs. Pressure

In liquids, molecules are closely packed. As pressure increases, molecules are forced even closer together. This enhances the intermolecular forces between them, making it harder for molecules to move past each other. Consequently, the resistance to flow (viscosity) of most liquids increases with increasing pressure.

Gas Viscosity vs. Pressure

In gases, viscosity arises from the transfer of momentum between layers due to molecular motion. At low pressures, increasing pressure leads to more frequent collisions but also a higher density, which initially decreases viscosity. However, at very great pressures, the gas molecules are compressed significantly, behaving more like a liquid. The reduced intermolecular distances and increased interactions cause the viscosity of gases to increase, similar to liquids.

Conclusion

Therefore, under very great pressures, the viscosity of most gases and liquids tends to increase.

The correct option is increases.