Based on the English alphabetical order, three of the following four letter-cluster pairs are alike in a certain way and thus form a group. Which letter-cluster pair DOES NOT belong to that group?
(Note: The odd one out is not based on the number of consonants/vowels or their position in the letter-cluster.)

​Logic: 1st - 2 = 2nd , 3rd- 2 = 4th 

Lets check each options

Option A: KL - PO

K +1 = L

P -1 = O
(does not follow)

Option B: HF - CA

H -2 = F

C -2 = A

Option C: LJ - GE

L -2 = J

G -2 = E

Option D: QO - LJ

Q -2 = O

Thus, correct option is (a).

L -2 = J