IMO C
arrange the set

-2 1 5 8

1) The median of the numbers in S is less than 5.
for n=0, -2 0 1 5 8 median is 1
for n=4, -2 1 4 5 8 median 4
NOT SUFF

2)The median of the numbers in S is greater than 1

for n=4, median greater than 1
for n=100, -2 1 5 8 100, median greater than 1
NOT SUFF

combined

for n=1,2,3,4
-2 1 n 5 8- satisfies the condition
for values <=0, median will be 1- ruled out
for value >4, median will be >=5, ruled out
so n=1,2,3,4. SUFF