Question

the activation of olfactory receptors requires that the odorant become immersed in mucus blood cerumen saliva

Explanation:

Olfactory receptors are located in the nasal cavity. Odorants (smell molecules) must dissolve in the mucus layer covering the olfactory epithelium to interact with the olfactory receptor neurons. Mucus provides the aqueous environment necessary for this interaction. Blood is not directly involved in the immediate activation process at the receptor level. Cerumen is earwax and has no role in olfaction. Saliva is related to taste (gustation) in the oral cavity, not olfaction (smell) in the nasal cavity.

Answer:

mucus