Which of the following is an example of a nontoxic chemical repellent?

Hotfoot is considered a nontoxic chemical repellent because it is designed to deter pests without utilizing harmful or toxic substances that could pose a risk to human health, pets, or the environment. Nontoxic repellents are generally formulated with ingredients that are safe for use around people and animals, making them a favorable choice for pest control in various settings, especially in homes and gardens.

In contrast, the other options contain chemicals that can be harmful. Chlorpyrifos is an organophosphate insecticide known for its toxicity to humans and wildlife, while Pyrethrin, although derived from chrysanthemum flowers and considered less toxic than some synthetic pesticides, can still have toxicity concerns for certain insects, aquatic life, and in higher concentrations. Boric acid, while commonly used as a pest control agent, can also be toxic to pets and humans if ingested in significant amounts. Therefore, Hotfoot stands out as the safest option among the choices provided for those seeking an effective yet nontoxic way to repel pests.