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 - 3 = 2nd letter, 2nd letter + 5 = 3rd letter and 3rd letter + 4 = 4th letter

Now, we check each options.

Option (a): KHMQ (Follow)

K - 3 = H, H + 5 = M, M + 4 = Q

Option (b): PMRV (Follow)​

P - 3 = M, M + 5 = R, R + 4 = V

Option (c): AXCH (Not Follow)​

A - 3 = X, X + 5 = C, C + 4 $$\neq$$ H​

Option (d): HEJN (Follow)​

H - 3 = E, E + 5 = J, J + 4 = N

Thus, correct option is (c).