Which of these has the highest permeability in a resting nerve cell?

The correct option is K+ (Potassium ions).

To understand why potassium ions (K⁺) have the highest permeability in a resting nerve cell, let's break down the physiology of the resting membrane potential step-by-step:
1. Selective Permeability of the Cell Membrane: The cell membrane of a resting neuron is not equally permeable to all ions. It contains specific, non-gated ion channels (often called leak channels) that remain open even when the neuron is at rest.
2. Abundance of Leak Channels: In a resting nerve cell, there are far more leak channels specifically designed for potassium (K⁺) than there are for sodium (Na⁺) or chloride (Cl^-). Typically, the membrane is about 25 to 100 times more permeable to K⁺ than to Na⁺.
3. Establishment of resting potential: Because of this high permeability, K⁺ ions readily diffuse out of the cell down their chemical concentration gradient (from high concentration inside to low concentration outside). This outward movement of positive charge is the primary driver in establishing the negative resting membrane potential (around -70 mV).