If the distilling plant first stage absolute pressure is higher than normal, while the second stage absolute pressure remains satisfactory, the probable fault is due to __________.

Correct Answer: Option B — an air leak through a vacuum gage line in the first stage

An air leak in the first stage of a multi-stage distilling plant increases the absolute pressure by introducing non-condensable gases. This disrupts the vacuum required for efficient evaporation. Since the second stage remains unaffected, the fault is isolated to the first stage's vacuum integrity, specifically the gauge lines or seals.