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Classic community-acquired pneumonia typically presents on a chest X-ray as lobar consolidation, which is often localized to one lobe of the lung. This consolidation results from alveolar filling with inflammatory exudate, leading to a dense, opaque appearance in the affected area. The X-ray may show air bronchograms, which are visible air-filled bronchi surrounded by opacified lung tissue, a common hallmark of this type of pneumonia.

Community-acquired pneumonia is primarily caused by pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, and other bacteria, often leading to this characteristic radiological finding. In contrast, atypical pneumonia tends to present differently on imaging, often exhibiting a more diffuse or interstitial pattern rather than lobar consolidation.

Pleural effusion may accompany pneumonia but is a secondary finding rather than a typical representation of classic community-acquired pneumonia. Similarly, pneumothorax is not related to pneumonia and appears as a presence of air in the pleural space, distinct from the consolidation seen in pneumonia.

Thus, the description of classic community-acquired pneumonia is encapsulated in the characteristic findings on a chest X-ray, making it the appropriate choice for this question.