Which of these activates an olfactory receptor and causes the transmission of information about a smell?

A. Papillae >>> on the tongue, taste buds.
B. Neurotransmitter >> YES
C. Cone cell >>> on eyes
D. Odorant >>> is what you smell, not causes the transmission

D. Odorant
An odorant is a molecule which binds to a receptor protein in the roof of the nasal cavity. Binding to the receptor causes an action potential (electrical signal) to be produced which then travels along the neuron. When the signal reaches the end of the neuron it stimulates release of a neurotransmitter which then binds to the next neuron and triggers another action potential in that neuron, so the signal continues to be transmitted until it reaches the brain.

Papillae are involved in taste, and cone cells are involved in sight.

Neurotransmitter