ANSWER :
C. The mean of the 6th and 7th values
EXPLANATION :
Median is the middle term when the data is arranged from smallest to largest.
From the problem, there are 12 values in a data set.
If we divide the set into two, that's
1 to 6 and 7 to 12
If you notice, there's NO middle term since the number of lower half (6 items) is the same with the number of upper half (6 items)
So we need to take the average or mean between the 6th and 7th term.