**Core Concept:** An inhibitory postsynaptic potential (IPSP) is a decrease in the membrane potential of a postsynaptic neuron caused by the arrival of a neurotransmitter at the synapse. IPSPs are typically mediated by the influx of chloride ions (Cl-) into the postsynaptic neuron.

**Why the Correct Answer is Right:** The correct answer (C) represents chloride ions, which are responsible for the generation of IPSPs. Inhibitory neurons release gamma-aminobutyric acid (GABA) or gamma-aminobutyric acid-A (GABAA) receptors at the synapse, leading to the opening of chloride channels and the influx of chloride ions into the postsynaptic neuron. This results in hyperpolarization and inhibition of the postsynaptic neuron.

**Why Each Wrong Option is Incorrect:**

A. Calcium (Ca2+) ions are responsible for generating excitatory postsynaptic potentials (EPSPs), not IPSPs.

B. Sodium (Na+) ions are involved in generating action potentials, not IPSPs.

D. Potassium (K+) ions are primarily responsible for generating action potentials, not IPSPs.

**Clinical Pearl:** Understanding the role of different ions in generating postsynaptic potentials is crucial for understanding synaptic transmission and neuronal communication. This knowledge is essential to comprehend the functioning of the nervous system, particularly in conditions where synaptic transmission is impaired (e.g., epilepsy, ataxia, or neuropathies) and to grasp the pharmacology of drugs like benzodiazepines, which modulate GABAA receptors and chloride channels.