Final answer:
During inhalation for a diaphragmatic breather, the area of the trunk that expands the most is the abdomen.
Step-by-step explanation:
When a client is a diaphragmatic breather, the area of the trunk that expands most during inhalation is the abdomen. During inhalation, the diaphragm contracts and moves downward, causing the abdominal cavity to expand. This movement allows the lungs to expand and fill with air. Other muscles, such as the external intercostals, assist in expanding the thoracic cavity and ribcage.