What is the reason for the unidirectional transmission of nerve impulses through a synapse?

Which of the following statements are correct regarding electrical synapses?
$i.$ At electrical synapses,the membranes of pre- and post-synaptic neurons are in very close proximity.
$ii.$ Electrical current can flow directly from one neuron into the other across these synapses.
$iii.$ Impulse transmission across an electrical synapse is very similar to impulse conduction along a single axon.
$iv.$ Electrical synapses transmit signals using neurotransmitters like acetylcholine.
$v.$ Electrical synapse transmission is very fast.
$vi.$ Electrical synapses are rare in our system.

Assertion : Transmission of nerve impulse across a synapse is accomplished by neurotransmitters.
Reason : Transmission across a synapse usually requires neurotransmitters because there is a small space,i.e.,synaptic cleft,that separates one neuron from another.

Which chemical substance is responsible for the transmission of nerve impulses across the synapse from one neuron to another?

How long does the synaptic delay last (in $, ms$)?

Axon endings release from their synaptic vesicles a neurotransmitter substance known as: