Which of the following is an example of chemical contamination in food?

Chemical contamination in food occurs when harmful substances, such as cleaning agents, pesticides, or food additives, inadvertently come into contact with food. The choice that exemplifies this well is when cleaning agents are left on food contact surfaces. If these surfaces are not properly rinsed after cleaning, remnants of chemicals can transfer to food, leading to health risks if consumed. This situation illustrates a direct and clear form of chemical contamination where food can absorb these toxic substances, making it unsafe for consumption.

The other options involve different types of contamination or food safety issues. Pest droppings represent biological contamination since they can introduce pathogens directly into food. Improper cooking techniques relate to physical contamination because they can compromise food safety by not eliminating harmful microorganisms. Undercooked meat is also a food safety issue, primarily related to biological risks, particularly pathogens such as bacteria that thrive in animal products when they are not cooked adequately.