The correct answer is (b). The first quartile is also known as the lower quartile. It is the value that divides the lower half of a data set into two equal parts. In other words, it is the value that separates the bottom 25% of the data from the top 75% of the data.
The median is the middle value in a data set. It is the value that divides the data set into two equal parts. The mode is the most frequent value in a data set. The third decile is the value that divides the data set into three equal parts.
Here is an example to illustrate the concept of the first quartile. Consider the following data set:
2, 3, 5, 7, 8, 9, 10, 11, 12, 13
The first quartile is the value that divides the lower half of the data set (2, 3, 5, 7) into two equal parts. In this case, the first quartile is 5. This is because 5 is the value that separates the bottom 25% of the data (2, 3) from the top 75% of the data (5, 7, 8, 9, 10, 11, 12, 13).