Which one of the following does not act as a neurotransmitter?

Given below are two statements.
Statement $I$ - In chemical synapse,the rate of transmission of impulse is higher in homeotherms than poikilotherms.
Statement $II$ - In chemical synapse,the synaptic cleft has a width of about $3.8 \ nm$.
In the light of the above statements,select the correct option given below:

Identify the sequential steps occurring in a chemical synapse.

Synaptic vesicles contain chemicals called

What is a neurotransmitter?

The cause of death in a person bitten by a cobra is: