(b) median
The middle-most observation of data arranged in order is called the median.
Source: Statistics, Section 13.4 (Median of Grouped Data), Chapter 13
The textbook explicitly defines median as "a measure of central tendency which gives the value of the middle-most observation in the data." Mode is the most frequent value, mean is the average, and deviation is not a measure of central tendency. For a 1-mark MCQ, just writing the option letter and the term is sufficient.