**Core Concept**
The normal distribution curve, also known as the Gaussian distribution or bell curve, is a probability distribution that is symmetric about its mean. It is characterized by its mean (μ) and standard deviation (σ). The normal distribution is often used to model continuous data in various fields, including medicine and statistics.

**Why the Correct Answer is Right**
The area between one standard deviation on either side of the mean in a normal distribution curve represents approximately 68.27% of the total area under the curve. This is because the normal distribution is symmetric, and the mean, median, and mode are all located at the center of the distribution. The area under the curve between one standard deviation on either side of the mean is often referred to as the "68-95-99.7 rule" or the "empirical rule." This rule states that about 68% of the data falls within one standard deviation of the mean, about 95% falls within two standard deviations, and about 99.7% falls within three standard deviations.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a correct answer because it does not accurately describe the area between one standard deviation on either side of the mean in a normal distribution curve.
* **Option B:** This option is not a correct answer because it is not a numerical value and does not accurately describe the area between one standard deviation on either side of the mean in a normal distribution curve.
* **Option D:** This option is not a correct answer because it is not a numerical value and does not accurately describe the area between one standard deviation on either side of the mean in a normal distribution curve.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the 68-95-99.7 rule is an approximation and may not hold true for all normal distributions. However, it is a useful rule of thumb for understanding the relationship between the mean, standard deviation, and the area under the normal distribution curve.

**Correct Answer:** C. 68.27%