Correct choice is (a) To supply moisture in the form of droplets
The explanation is: Nebulizers are used to convert the liquids into gaseous form and is sent on the respiratory path. This is also a method to deliver medicines in case of asthma attack, COPD etc. If the air does not contain a sufficient amount of moisture in it, it can cause a drying and desiccation of the respiratory track and pathway. This can cause problems like bleeding and injury. Thus, nebulizers are used to maintain moisture levels of the air.