The receptors of neurotransmitters are present on/in the

Which of the following does not act as a neurotransmitter?

Select the incorrect statement regarding synapses :

What happens if $GABA$ is released at the synapse?

Five events in the transmission of a nerve impulse across a synapse are given below:
$a.$ Certain ion channels open,allowing ions to enter and generate a new action potential in the post-synaptic neuron.
$b.$ Neurotransmitter molecules bind to receptors on the post-synaptic membrane.
$c.$ Synaptic vesicles fuse with the pre-synaptic membrane,and the neurotransmitter is released into the synaptic cleft. Depolarization of the pre-synaptic membrane is induced.
$d.$ An action potential reaches the axon terminal.
What is the correct sequence of these events?

The enzyme required for the conduction of nerve impulses across the synapse is: