## Core Concept
Alcohol intoxication leads to a spectrum of effects on the central nervous system, ranging from euphoria to incoordination and eventually to coma. The level of alcohol in the body at which incoordination occurs is related to the blood alcohol concentration (BAC), typically measured in grams per deciliter (g/dL) or milligrams per milliliter (mg/mL), which can also be expressed as a percentage.

## Why the Correct Answer is Right
Incoordination due to alcohol consumption typically starts to become evident at a blood alcohol concentration of about 0.05 to 0.10%. This level of alcohol affects the cerebellum, which is responsible for coordinating movements. The cerebellar effects of alcohol lead to ataxia (loss of muscle coordination) and incoordination. A blood alcohol level of **0.05%** (or 50 mg/dL) is often associated with the onset of such symptoms.

## Why Each Wrong Option is Incorrect
- **Option A:** 0.025% is a lower concentration and typically associated with feelings of relaxation and euphoria rather than incoordination.
- **Option B:** 0.03% might cause slight impairment but is generally below the threshold for significant incoordination.
- **Option D:** 0.15% is a higher concentration that would likely cause more severe impairment, including slurred speech, significant ataxia, and potentially loss of consciousness.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the effects of alcohol can vary significantly among individuals based on factors like body weight, tolerance, and the rate of consumption. However, a commonly taught threshold for the onset of incoordination and significant impairment is around **0.05%** BAC.

## Correct Answer Line
**Correct Answer: C. 0.05.**