Based on alphabetical order, three of the following four letter clusters…

Concept

Represent each letter by its alphabet position, with A = 1, B = 2, and so on up to Z = 26.

A letter cluster follows a constant-shift pattern when the same cyclic backward shift is applied between each pair of successive letters. When a shift crosses A, continue backward from Z.

Application

1. ROL corresponds to 18 → 15 → 12, so the two successive shifts are 3 places backward and 3 places backward.

2. DAX corresponds to 4 → 1 → 24, so the two successive shifts are 3 places backward and 3 places backward, with cyclic wrap-around from A to X.

3. JHD corresponds to 10 → 8 → 4, so the two successive shifts are 2 places backward and 4 places backward.

4. PMJ corresponds to 16 → 13 → 10, so the two successive shifts are 3 places backward and 3 places backward.

Cross-check and contrast

• ROL, DAX, and PMJ each use the same backward shift of 3 between both successive pairs.

• JHD instead uses two unequal shifts: 2 places backward and then 4 places backward.

Result

Therefore, JHD is the letter cluster that does not belong to the group.