What makes nitric oxide unique among neurotransmitters? Select one: a. It is an organelle. b. It is released before the action potential occurs. c. It is taken back up into the presynaptic neuron. d. It is a gas.

Answer: It is a gas

Explanation:

The most unique thing about nitric oxide being a neurotransmitter is that it is the only neurotransmitter which is in gaseous form.

Nitric oxide is small gaseous molecules which is synthesized by the de novo process in the neuronal tissue.

It can diffuse by plasma membrane.

It diffuses out of the postsynaptic neurons and acts on the neighboring neurons and presynaptic terminals to assist the generation of the Long Term potentiation.