Ans. is 'b' i.e., Air Bronchogram Absent Air bronchogram refers to the phenomenon of air filled bronchi (dark) being visible by the opacification of the surrounding alveoli (grey/white). Air bronchogram is common in consolidation or in any condition in which something replaces the air spaces. Air bronchogram commonly signifies alveolar disease (any cause of consolidation). On a normal radiograph, the bronchi are not normally visible. During consolidation the alveoli do not contain air due to the replacement of the air spaces. When the alveoli no longer contain and opacify, the air filled bronchi passing through the same area may be visible as branching lineur lucencies