Solution:The pattern followed here is :(1st letter + 3 = 2nd letter), ( 2nd letter + 1 = 3rd letter) & (3rd letter + 5 = 4th letter)
ADEJ → (A + 3 = D), (D + 1 = E) & (E + 5 = J)
LOPU → (L + 3 = O), (O + 1 = P) & (P + 5 = U)
FIJO → (F + 3 = I), (I + 1 = J) & (J + 5 = O)
But,
PSTZ → (P + 3 = S), (S + 1 = T) & (T + 5 ≠ Z)
Hence, PSTZ is the correct answer.