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