Final answer:
The lateral decubitus position, with the right side down, is optimal for demonstrating right lung pleural effusion on a radiograph. However, large effusions may also be visible in upright or anteroposterior views.
Step-by-step explanation:
The position that best demonstrates pleural effusion of the right lung on a radiograph is when the patient is in the lateral decubitus position, with the right side down. In this position, free fluid in the pleural space can layer out and is more easily visualized. A chest radiograph might show a meniscus sign which is suggestive of a pleural effusion. However, pleural effusions can also be identified in an upright or anteroposterior position if the effusion is large. The presence of lung infiltrates on a chest radiograph, suggestive of pneumonia, typically shows as opaque patches within the lung fields, which can sometimes be confused with pleural effusion if not properly delineated by imaging or clinical correlation.