Three of the following four letter-clusters are alike in a certain way and one Pick the odd one out.

JIG

1   2    3    4   5    6   7     8    9  10  11  12  13

 A   B   C    D   E    F   G    H    I    J    K    L   M

 ↓    ↓    ↓    ↓    ↓     ↓   ↓    ↓     ↓   ↓    ↓    ↓    ↓

 Z   Y    X   W   V    U   T    S    R   Q   P    O   N

26  25  24  23  22  21  20  19  18  17  16  15  14

THE LOGIC FOLLOWED HERE IS;

(Difference between the positional value of 1st letter and 2nd letters is (-2))

(Difference between the positional value of 2nd letter and 3rd letters is (-2))

So,

1) FDB,

F → (-2) → D

D → (-2) → B

2) ZXV,

Z → (-2) → X

X → (-2) → V

3) JIG,

J → (-1) → I

I → (-2) → G

Thus, JIG  does not belong to that group.