Certified Pulmonary Function Technologist (CPFT) Practice Exam

The Geissler tube ionizer is primarily designed for the analysis of gases, and it is particularly effective with noble gases, including helium. The function of the Geissler tube relies on the ionization of gas molecules when subjected to high-voltage electric fields. In the context of the question, while nitrogen could potentially be assessed, it is not the primary focus of a Geissler tube ionizer.

Helium, as a noble gas, is frequently utilized in Geissler tubes. Its low ionization energy makes it readily ionized under electrical discharge conditions. This property allows for effective measurement and analysis of helium gas within the tube. The ability of the Geissler tube to analyze this specific gas emphasizes its role in demonstrating phenomena associated with gases that easily ionize and conduct electricity.

Therefore, focusing on the primary function and design of the Geissler tube, helium is the correct answer as it aligns with the fundamental principles governing how this equipment operates.