Which of these easily observed molecular species is used as a tracer for the fundamental but difficult to observe H₂ molecules in giant molecular clouds?

Question

Quizplus · Accepted Answer

Carbon monoxide (CO) is commonly used as a tracer for molecular hydrogen (H₂), which is difficult to observe directly in interstellar space due to its lack of a permanent electric dipole moment. CO, with its strong dipole moment, is more easily detected and its abundance can be used to infer the presence and quantity of H₂ in giant molecular clouds.

Which of These Easily Observed Molecular Species Is Used as a Tracer