Final answer:
The synonym for contagiousness that refers to the ability of a disease to spread from one person to another is infectiousness. Therefore, the correct option is 2.
Step-by-step explanation:
The synonym for contagiousness is Infectiousness, which refers to the capability of a disease to be transmitted from one person to another. This term is often used when discussing pathogens and their ability to cause infectious diseases. Infectious diseases can be contagious during various periods, with some being more likely to spread at different stages depending on the disease and the mechanism of transmission. For instance, respiratory infections are typically contagious during the prodromal period, whereas patients with viral meningitis are contagious when symptoms begin to appear, and diseases like measles can be contagious even during the incubation period before symptoms are present.