Which of the following is a UN number for an Infectious Substance?

UN3373 is indeed the correct UN number for Infectious Substances. This number specifically designates biological substances that can contain pathogens or biological agents that may cause disease in humans or animals, such as certain medical waste or specimens collected for diagnostic purposes. The classification under this UN number includes criteria that outline how these substances must be handled, packaged, labeled, and transported to ensure safety and compliance with regulatory standards.

The other UN numbers represent different categories of dangerous goods. UN1845, for example, refers to a different type of substance, typically involving flammable solids. UN4042 encompasses various types of substances, possibly including environmental concerns but not infectious materials. UN1015 is designated for a specific gas, which is entirely separate from the infectious substances category. Thus, UN3373 stands out as the only correct answer relating specifically to Infectious Substances in this context.