Ans. is 'c' i.e Foreign Body Aspiration Foreign Body Aspiration :It is an important cause of stridor in children.If obstruction occurs it leads to hyperinflation.The overlying chest wall shows hyperresonance.There will be decreased breath sounds.All the other choices mentioned in the question do not cause stridor.Asthma - It is bilateral, There is no stridor (wheezing is present)Aspiration Pneumonia - In Pneumonia there is consolidation of the lung, instead of hyperinflation there is dullness present.Pleural effusion - Dullness is present instead of Hyperinflation. PercussionBreath soundVoice transmissionAdventitious soundForeign body aspirationHyperresonantDecreased Aspiration pneumoniaDullDecreasedDecreasedAbsentAsthmaHyperresonantVesicularNormalWheezingPleural effusionDullDecreasedDecreasedAbsent or pleural friction rubPneumothoraxDullDecreasedDecreasedAbsent or pleural friction rubEmphysemaHyperresonantDecreasedDecreasedAbsent or wheezing