Final answer:
The correct answer is option 2. Solanine found in the green skin of potatoes exposed to light is an example of a naturally occurring toxin in foods. It is one of the various toxins that can contaminate foods, and other examples include botulism toxin by microorganisms and mercury in fish.
Step-by-step explanation:
An example of a toxin that can occur naturally in foods is solanine in the green skin of potatoes exposed to light. Solanine is a glycoalkaloid poison found in species of the nightshade family, like potatoes and tomatoes, and it can develop when they are exposed to light and begin to turn green. This natural toxin can cause nausea, diarrhea, and headache if consumed in large quantities.
Toxins in food can also come from a variety of other sources, for example, toxins produced by microorganisms such as the botulism toxin from Clostridium botulinum, or those produced by fungi like the aflatoxin which targets the liver. Another example of natural toxins in food includes mercury that accumulates in tuna fish due to environmental contamination. However, among the options provided, the presence of solanine in the green portions of potatoes is the correct example of a naturally occurring toxin in food.