Synaptic cleft a- is the space between two synapses on the surface of neuronsb- allow diffusion of transmitters between neuronsc- is filled with intracellular fluidd- ranges between 20 – 30 μm in width

The synaptic cleft is a small gap at the end of a neuron that allows a signal to pass from one neuron to the next. Here are the answers to your options:

a- Incorrect. The synaptic cleft is not the space between two synapses on the surface of neurons. It is the space between the end of a neuron and the start of another.

b- Correct. The synaptic cleft allows the diffusion of neurotransmitters, which are chemicals that transmit signals across a synapse from one neuron to another.

c- Incorrect. The synaptic cleft is not filled with intracellular fluid. It is an extracellular space filled with a matrix of fibrous proteins.

d- Incorrect. The width of a synaptic cleft is approximately 20-40 nanometers, not 20-30 micrometers.