When testing boiler flue gas with a chemical absorption apparatus, to obtain accurate results __________.

Correct Answer: Option D — prevent any air from contaminating the gas sample

Chemical absorption flue gas analyzers, such as Orsat apparatuses, rely on precise volumetric gas measurements. Preventing any ambient air contamination during sampling is vital, as even minor air leaks skew oxygen and carbon dioxide percentages, resulting in erroneous combustion calculations.