Which of the following is a sign of food spoilage?

Off smells are a clear indication of food spoilage because they signal the presence of bacteria or other microorganisms that have begun to break down the food. These smells often result from the production of gases or byproducts during the decomposition process. If food emits an unusual or unpleasant odor, it is a strong sign that its safety and quality have been compromised, suggesting it's no longer safe for consumption.

Bright colors, firm texture, and chilled temperatures, on the other hand, are typically associated with fresh, safe food. Bright colors can indicate freshness and ripeness, firm texture often means the food has not deteriorated, and maintaining a chilled temperature is an important factor in keeping food safe from spoilage.