What is a key characteristic of a supercritical fluid?

A supercritical fluid is indeed characterized by its ability to exhibit properties of both gases and liquids. This unique state occurs when a substance is subjected to temperatures and pressures above its critical point. In this state, a supercritical fluid can diffuse through solids like a gas while dissolving materials like a liquid. This dual behavior is particularly useful in applications such as extraction processes, where the fluid can penetrate materials efficiently and selectively dissolve certain compounds.

The other options do not accurately capture this defining characteristic of supercritical fluids. While supercritical fluids may have low viscosity compared to liquids, they do still possess viscosity; thus, claiming that they have no viscosity would be misleading. Additionally, while many supercritical fluids, such as supercritical carbon dioxide, are often colorless and odorless, this is not a universal trait applicable to all supercritical fluids. Lastly, supercritical fluids do not freeze at room temperature; rather, they exist in their supercritical form only under specific temperature and pressure conditions.