Which of the following is an example of a physical food hazard?

A physical food hazard refers to any foreign object that can potentially cause harm when it is present in food. In this context, long nails are considered a physical hazard because they can break off and end up in food, posing a choking risk or injury to someone consuming the contaminated food. This scenario underscores the importance of maintaining hygiene standards and ensuring that food handlers keep their nails trimmed and clean to avoid such hazards.

In contrast, other options represent different categories of food hazards: contaminated water is considered a chemical hazard, improper cooking temperature falls under biological hazards due to the risk of foodborne pathogens, and expired ingredients are typically viewed as quality hazards rather than physical hazards. Each type of hazard requires specific preventive measures to ensure food safety, but in this case, long nails clearly exemplify the nature of a physical hazard.