Final answer:
The parasympathetic receptor on ganglionic neurons causing excitation is the c) nicotinic receptor, which is a ligand-gated ion channel that results in depolarization when activated by acetylcholine.
Step-by-step explanation:
The parasympathetic receptor found on ganglionic neurons that causes excitation is the nicotinic receptor. All ganglionic neurons of the autonomic system, including both sympathetic and parasympathetic ganglia, are activated by acetylcholine (ACh) released from preganglionic fibers.
The ACh receptors on these neurons are of the nicotinic type, which are ligand-gated ion channels leading to depolarization upon neurotransmitter binding. In summary, the correct answer to the question is (c) nicotinic.