Final answer:
Mucolytic agents are best for a patient with thick pulmonary secretions, as they thin and loosen mucus to aid in clearing the airways. Thus, the option "3" is the correct answer.
Step-by-step explanation:
For a patient with difficulty breathing due to airways obstructed by thick pulmonary secretions, the nurse would expect mucolytic agents to be most beneficial. These medications help to thin and loosen the mucus, making it easier to expel from the airways. Unlike antibiotics, which are used to treat bacterial infections, or corticosteroids and leukotriene modifiers, which reduce inflammation and allergic reactions respectively, mucolytics directly target the viscosity of mucus to enhance clearance from the lungs.