The items labeled "21" and "22", shown in the illustration are used to remove __________. Illustration MO-0111

Correct Answer: Option D — non-condensable gases and brine

Items '21' and '22' are extraction devices used to maintain the efficiency of the distillation process. They are specifically designed to remove non-condensable gases, which would otherwise insulate the tubes and degrade heat transfer, and to purge concentrated brine, which prevents scale formation and maintains the required water purity.