Okay, let's tackle this question. The user provided a question about the normal standard curve and one standard deviation. First, I need to recall what the normal distribution curve entails. In statistics, the normal distribution is a bell-shaped curve where most data points cluster around the mean. The standard deviation measures the spread of the data.

The question is asking what percentage of data falls within one standard deviation from the mean. From what I remember, in a normal distribution, about 68% of the data lies within ±1 standard deviation, 95% within ±2, and 99.7% within ±3. That's the empirical rule, also known as the 68-95-99.7 rule. So the correct answer here should be 68%.

Now, the user mentioned that the options A to D are missing. But since the correct answer is supposed to be one of them, I can infer that the options likely include 68%, 95%, 99.7%, and maybe a distractor like 50%. The incorrect options would be the other percentages. For example, if an option says 95%, that's two standard deviations, not one. Similarly, 99.7% is three. The 50% is probably a trick option.

I need to explain why each wrong option is incorrect. For Option A (if it's 95%), that's two SDs. Option B (if 99.7%) is three SDs. Option C (50%) is not part of the empirical rule. The clinical pearl here is to remember the 68-95-99.7 rule. It's high-yield for statistics in medical exams. Students might confuse the percentages with different standard deviations, so emphasizing the exact numbers is key.

**Core Concept**
The normal standard curve (Gaussian distribution) describes how data is distributed around the mean in a population. One standard deviation (SD) from the mean encompasses **68%** of the data in a normally distributed dataset. This is part of the **empirical rule** (68-95-99.7 rule), which is critical for interpreting statistical results in clinical research.

**Why the Correct Answer is Right**
In a normal distribution, **68% of values lie within ±1 SD** of the mean. This is a foundational statistical principle used to assess variability and probability. For example, if a lab test has a mean of 100 and SD of 15, 68% of results will fall between 85 and 115. This is mathematically derived from the integral of the normal distribution curve between -1σ and +1σ.

**Why Each Wrong Option is Incorrect**
**Option A:** Likely represents 50% (incorrect, as this is not a standard deviation boundary in normal distribution).
**Option B:** Likely represents 95% (incorrect, as this corresponds to ±2 SDs, not 1 SD).
**Option C:** Likely represents 99.7% (incorrect, as this corresponds to ±3 SDs, not 1 SD).

**Clinical Pearl / High-Yield Fact**
**Memorize the 68-95-99.7 rule**:
- 68%

✓ Correct Answer: B. 68%