What indicates a dent in the case of ammunition?

The indication of a dent in the case of ammunition is best represented by a dimple or depression. A dent typically refers to a localized deformation in the material, which manifests as a concave area where the metal has been pushed in without breaking the surface. The term "dimple" is specifically used to describe such small depressions, making it the most accurate option among the choices.

While a scrape or indentation may suggest some surface disruption, it doesn't specifically convey the idea of a dent, which is more characterized by a lack of material rather than just a surface alteration. An actual tear or rip indicates a more severe form of damage where the material has been compromised or separated, leading to a different kind of failure in the ammunition casing. A layer of oxidation refers to surface corrosion, which does not imply any mechanical denting but rather a change in the surface condition due to environmental exposure. Consequently, the presence of a dimple or depression explicitly aligns with the definition of a dent in the context of ammunition cases.