Final answer:
Influenza is the infectious disease spread by droplets < 5 microns in size.
Step-by-step explanation:
The infectious disease that is spread by droplets < 5 microns in size is Influenza. Influenza is an airborne disease that spreads through respiratory droplets when an infected person coughs, sneezes, or talks. These droplets can then be inhaled by another person and cause infection.
For example, if a person with influenza coughs without covering their mouth, the small droplets containing the virus can travel through the air and enter the respiratory system of a nearby person.
Other infectious diseases mentioned in the options, such as Respiratory syncytial virus, Tuberculosis, and Hepatitis A, are spread through different modes of transmission, not through small droplets in the air.
Learn more about Infectious diseases transmitted by droplets