**Core Concept**
Skeletal muscle paralysis is a potential complication of severe hypokalemia, which occurs when serum potassium levels drop below a critical threshold. This phenomenon is closely related to the pathophysiology of muscle membrane excitability and the role of potassium ions in maintaining the resting membrane potential.

**Why the Correct Answer is Right**
The critical level of serum potassium at which paralysis becomes a possible complication of hypokalemia is around 2.5 mEq/L. At this level, the muscle membrane becomes increasingly depolarized, leading to a decrease in the safety factor for action potential generation. As a result, even minor stimuli can trigger muscle contraction, and the muscle becomes more susceptible to fatigue and paralysis. This is because potassium ions play a crucial role in maintaining the resting membrane potential and regulating the excitability of skeletal muscle cells.

**Why Each Wrong Option is Incorrect**
**Option A:** A serum potassium level of 2.0 mEq/L is significantly lower than the threshold for paralysis and would likely result in more severe muscle weakness and fatigue.

**Option C:** A serum potassium level of 3.0 mEq/L is still within the normal range and would not typically cause muscle paralysis.

**Option D:** A serum potassium level of 3.5 mEq/L is actually above the normal range and would not cause muscle paralysis.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the clinical consequences of hypokalemia can vary depending on the severity and duration of the potassium deficit. Mild hypokalemia may be asymptomatic, while severe hypokalemia can lead to muscle weakness, paralysis, and even cardiac arrhythmias.

**✓ Correct Answer: B. Serum Potassium at 2.5 mEq/L**