What visual indication typically implies that an item is very dense on an X-ray scan?

In an X-ray scan, the visual representation of various materials is based on their density and atomic number. The correct answer indicates that materials with a higher density appear darker on an X-ray image, which corresponds to blue to black colors. This is because denser items absorb more X-rays, preventing them from reaching the X-ray film or detector, thus appearing as darker shades on the resulting image.

In contrast, materials that are less dense will permit more X-rays to pass through, resulting in lighter colors on the scan. This understanding is crucial for accurate interpretation of X-ray images, particularly in security and law enforcement contexts, where identifying potentially hazardous items is essential.