Answer: c) Signal transmission occurs by diffusion of a compound called a neurotransmitter through the intercellular space between neurons
A chemical synapse refers to a gap between two neurons, through which electrical signals must pass.
Neurotransmitters are mobile compounds that are responsible for passing signals across neurons, through a synapse. They pass through the intercellular spaces between the neurons and form a bridge of some sort between the two neurons separated by a gap. The signals that need to be sent across then have easy access to the next or target neuron.