The correct option is: b. 3
<u><em>Explanation</em></u>
Middle 50% data means the "Interquartile Range" which is measured as the difference between the third quartile and the first quartile in a data set.
In the given box plot, we can see that: and
So, the Interquartile range,
Thus, the range of the middle 50% of data will be 3.