Concentrated hydrochloric acid when kept in open air sometimes produces a cloud of white fumes. The explanation for it is that

• A
  Concentrated hydrochloric acid emits strongly smelling $HCl$ gas all the time
• B
  Oxygen in air reacts with the emitted $HCl$ gas to form a cloud of chlorine gas
• C
  Strong affinity of $HCl$ gas for moisture in air results in forming of droplets of liquid solution which appears like a cloudy smoke
• D
  Due to strong affinity for water,concentrated hydrochloric acid pulls moisture of air towards itself. This moisture forms droplets of water and hence the cloud