**Core Concept**
Blood alcohol level (BAL) is a critical factor in assessing the severity of alcohol intoxication. The BAL is expressed as grams of alcohol per 100 milliliters of blood. Different levels of BAL are associated with various symptoms, including Nystagmus, slurred speech, and blackouts.

**Why the Correct Answer is Right**
The BAL at which Nystagmus, marked slurring of speech, and alcoholic blackouts occur is typically between 200-300 mg/dL. This level of intoxication affects the central nervous system, leading to impaired motor coordination, speech, and cognitive functions. The presence of Nystagmus, a rhythmic, involuntary eye movement, is a specific indicator of high BAL, often seen in individuals with a BAL above 200 mg/dL. The mechanism behind this involves the inhibition of the inhibitory neurotransmitter GABA and the stimulation of excitatory neurotransmitters such as glutamate.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the BAL associated with mild intoxication, such as 50-100 mg/dL, typically presents with symptoms like euphoria, relaxation, and minor impairment in motor coordination.

**Option B:** This option is also incorrect because a BAL of 150-200 mg/dL is associated with more pronounced symptoms, including impaired judgment, impaired motor coordination, and slurred speech, but not typically Nystagmus.

**Option C:** This option is incorrect because a BAL of 300-400 mg/dL is associated with severe intoxication, which can lead to respiratory depression, coma, and even death.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the BAL can be estimated using the Widmark formula, which takes into account the individual's weight, the amount of alcohol consumed, and the time frame over which the alcohol was consumed. However, this formula is not as accurate as actual BAL measurement.

**Correct Answer: C. 300-400 mg/dL**