The pattern Followed here is:
The Series consists of 3 different series within it.
D, F, J, P, X, U, H with difference of +2, +4, +6, +8, +10
4, 8, 12, 16, 20, 24 with the difference of +4.
A, F, (K), P, U, (Z) with a difference of +5
Hence, the correct answer is "The first bracketed letter is correct and the second bracketed letter is incorrect.".