Which of the following substances would be classified as infectious waste?

Infectious waste is defined as any waste that contains pathogens or other potentially harmful agents capable of causing disease in humans or animals. In this context, Petri plates and scalpel blades are considered infectious waste because Petri plates may contain bacterial or viral cultures, which are viable and potentially infectious. Meanwhile, scalpel blades, which are sharp objects that can be contaminated with blood or other bodily fluids, pose a risk of transmitting infections if not handled or disposed of properly.

The other options consist of items that do not carry the same level of infectious risk. Diapers and sanitary napkins may be regarded as biohazardous in some contexts due to the potential for blood or bodily fluid content, but they are not categorized as infectious waste in a clinical sense. Facial tissues, while they can carry some germs, are typically not classified as infectious waste because they are not associated with high-risk pathogens. Cardboard and wood do not present infectious risks and are considered general waste. Therefore, Petri plates and scalpel blades are the clear examples of substances that are classified as infectious waste due to their direct association with laboratory and clinical practices that involve pathogens.