Chest X-ray shows opacity after blunt trauma, most likely diagnosis is –
Haemothorax
Pneumothorax
Pneumonia
Pulmonary embolism
Amongst the given options hemothorax and pneumonia (consolidation) produce opacity on chest X-ray. Pneumonia has nothing to do with blunt chest trauma, while hemothorax is common after blunt chest trauma. Therefore, best answer here is hemothorax.
Pneumothorax causes hypertranslucency (not opacity).