Give a tight upper bound deterministic selection n = 25 set of 25 elements contain elements

For n = 25, give a tight upper bound on the size of L. In other words, find the value k such that both of the following conditions hold:

a) abs (L) will always be ≤ k when n = 25

b) there is a set S of 25 elements for which L does indeed contain k elements.

Justify your answer. How does this compare with the upper bound?