Which one of the following pesticides can be legally used in the United States by the public?

The correct answer pertains to Diazinon, which has been sold in the United States for certain uses by the public. This pesticide was commonly used for controlling various pests in residential settings, including insects that affect gardens and lawns, as well as in some agricultural applications.

While it's important to recognize that Diazinon has been subject to increased regulation due to concerns about its toxicity and environmental impact, it remains a legal option for public use under specific restrictions.

Malathion can also be used legally by the public, but it is often subject to stricter application guidelines and may not be available for all uses that homeowners would typically need. Chlordane and Aldicarb, on the other hand, have been banned for residential use due to their harmful effects on human health and the environment. Chlordane, a persistent organic pollutant, is no longer permitted for use after its ban in the 1980s, and Aldicarb has severe restrictions and is primarily limited to agricultural applications under stringent regulations.

Thus, Diazinon stands out as the pesticide that legally remains available for certain public usages as of the latest regulations before October 2023.