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 letter + 4 and 2nd letter + 6 place.
Now, we check each options.
​Option (a): ​KH – OM

K + 4 = O, H + 6 $$\ne$$ M​
​Option (b): ​MG – QM

M + 4 = Q, G + 6 = M
​Option (c): ​YJ – CP

Y + 4 = C, J + 6 = P
​Option (d): ​LB – PH

L + 4 = P, B + 6 = H

Thus, correct option is (a).