<prompt> Croup N most commonly due to -The respiratory syncytial virusThe para influenza virusThe adenovirusThe coronavirus  <response>: Ans. is b i.e., The para influenza virus Croup Laryngotracheobronchitis Croup is a viral infection of upper respiratory tract. Children between the age of 1-5 years are affected. Para-influenza type I virus is the most common causative organism. Other viruses implicated in causaction are RSV, influenza virus, Adneovirus and Rhinovirus. 