What is a type of fossil formed when an organism buried in sediment dissolves, leaving a hollow area?

A mold fossil is created when an organism is buried in sediment and subsequently dissolves, leaving behind a hollow impression or cavity in the sediment where the organism used to be. This process can occur in various sediments, such as mud, sand, or volcanic ash, and is typically facilitated by natural processes over time, including the action of water and other geological forces.

In contrast, a cast fossil is formed when the mold is later filled with mineral-rich water that hardens, creating a replica of the original organism. Imprints are surface impressions of an organism, like footprints or leaf patterns, and trace fossils represent evidence of the organism's activity, such as burrows or bite marks, rather than the organism itself. These distinctions clarify why the correct choice is mold, as it specifically addresses the scenario of an organism leaving behind a hollow area in the sediment after dissolving.