Final answer:
The most likely diagnosis based on the given information is pneumonia, which is characterized by consolidation and opacities on the chest radiograph.
Step-by-step explanation:
The most likely diagnosis based on the given information is pneumonia. The presence of a "3" sign with notching of the ribs on a CXR is indicative of pneumonia. In pneumonia, the lung infiltrates with fluid or pus, leading to consolidation and opacities on the chest radiograph. This is seen as white areas within the lung that should otherwise be black. Pneumonia can be caused by bacterial, viral, or fungal infections.