Final answer:
Of the chemicals listed, Malathion would likely be the least toxic to humans, as it is used for controlling mosquitoes and poses relatively lower mammalian toxicity in comparison to other, more toxic organophosphates.
Step-by-step explanation:
Among the listed options, chemicals such as TEPP, Methyl Parathion, and HETP are all organophosphates, which are known to be highly toxic substances. They can poison thousands of humans annually and cause acute toxicity and death at high enough doses. Malathion, part of the same family, has relatively low mammalian toxicity and is used worldwide to help control mosquito populations and other pests. Given its lower toxicity profile in comparison to other organophosphates such as Parathion (which is 30 times more toxic than DDT), Multihion (which does not appear in the provided reference and therefore cannot be accurately compared), and TEPP, which is another highly toxic organophosphate, Malathion would likely be the least toxic to humans of the options provided.