What type of medication is used to relieve respiratory distress by widening air passages?

A bronchodilator is the correct choice for relieving respiratory distress by widening air passages. These medications work by relaxing the muscles of the airways, which helps to open them up and make it easier for an individual to breathe. This is particularly useful in conditions such as asthma or chronic obstructive pulmonary disease (COPD), where airway constriction can lead to difficulty in breathing.

Expectorants are used to help clear mucus from the airways, aiding in productive coughs but are not primarily focused on widening air passages. Antitussives are medications that suppress cough, and while they may provide some relief for coughing, they do not address the underlying airway constriction. Antihistamines are used to treat allergic reactions and may reduce congestion but do not directly widen the air passages like bronchodilators do. Therefore, when the goal is to relieve respiratory distress specifically through the dilation of the airways, bronchodilators are the most effective choice.