Which of the following is an example of a phytochemical?

Beta-carotene, found in carrots, is classified as a phytochemical because it is a naturally occurring compound produced by plants. Phytochemicals are known for their potential health benefits, including antioxidant properties, which help to protect the body from oxidative stress. Beta-carotene specifically is a precursor to vitamin A and plays a crucial role in vision, immune function, and skin health.

The other options represent different categories of nutrients. Vitamin C is a water-soluble vitamin essential for various bodily functions but does not qualify as a phytochemical. Calcium and iron are minerals that play vital roles in bodily functions, but they also do not fall under the definition of phytochemicals, which are primarily plant-derived compounds. Thus, beta-carotene stands out as the correct answer due to its origins and health benefits associated with plant consumption.