The mode of the data set is 11.
The mode is the data value that occurs most often. To find the mode, list all of the data values and count the number of times each data value repeats; the data value with the most repeats is the mode. In this data set, 11 occurs twice while all other data values occur only once.
87 occurs 1 time
19 occurs 1 time
52 occurs 1 time
11 occurs 2 times