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 + 3 = 3rd letter and 2nd letter + 3 = 4th letter

Now, we check each options.

Option (a): GK - JN (Follow)

G + 3 = J, K + 3 = N

Option (b): EI - HL (Follow)​

E + 3 = H, I + 3 = L

Option (c): ML - KJ (Not Follow)​

M + 3 $$\neq$$​ K, L + 3 $$\neq$$​ J

Option (d): LP - OS (Follow)​

L + 3 = O, P + 3 = S

Thus, correct option is (c).