Which of the following qualities of iodinated contrast contributes to discomfort and side effects?

Viscosity refers to a fluid's resistance to flow, which significantly influences how a contrast agent feels when injected and how it interacts within the body. High-viscosity contrast agents can cause discomfort during administration, as they may take more effort to inject and can lead to a sensation of heaviness or pressure at the injection site. This can also affect the speed at which the contrast moves through the vascular system, potentially contributing to side effects such as a sense of warmth or flushing.

While color, density, and flammability might have relevance in other contexts, they do not directly relate to the immediate sensations or side effects associated with the administration of iodinated contrast media. Color typically does not affect patient comfort or side effects, density is more about the concentration and has little to do with discomfort, and flammability is not a concern with iodinated contrast used in medical imaging procedures. Therefore, viscosity stands out as the key quality impacting patient experience.