​Based on the English alphabetical order, three of the following four letter-clusters are alike in a certain way and thus form a group. Which letter-cluster 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 = 2nd letter and 2nd letter - 6 = 3rd letter
Now, we check each options.
​Option (a): HLF (Follow)

H + 4 = L, L - 6 = F
​Option (b): ​MQK​ (Follow)​

M + 4 = Q, Q - 9 = K
​Option (c): ​KOI​ (Follow)​

K + 4 = O, O - 6 = I 
​Option (d): ​FJC​ (Not Follow)​

F + 4 = J, J - 6 $$\neq$$​ C
Thus, correct option is (d). ​