**Core Concept**
The median is the middle value of a data set when it is arranged in ascending or descending order. It is a measure of central tendency, used to describe the distribution of a set of numbers. In a dataset with an even number of observations, the median is the average of the two middle values.

**Why the Correct Answer is Right**
To find the median, we first arrange the given data in ascending order: 5, 5, 10, 20, 50, 150. Since there are 6 observations (an even number), the median will be the average of the two middle values, which are 10 and 20. Therefore, the median is (10 + 20) / 2 = 15.

**Why Each Wrong Option is Incorrect**
* **Option A:** There is no indication that the data is skewed or that the median is not the middle value.
* **Option B:** The mode is the value that appears most frequently, but it is not the same as the median.
* **Option C:** The range is the difference between the largest and smallest values, but it does not describe the central tendency of the data.

**Clinical Pearl / High-Yield Fact**
When dealing with a dataset, it's essential to understand the difference between the mean, median, and mode. The mean is sensitive to extreme values, while the median is a better representation of the central tendency in skewed distributions.

**Correct Answer: B. 15.**