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.)

The correct option is FJC.

To determine which letter-cluster does not belong to the group, let us analyze the positional values of each letter in the English alphabet:

A = 1, B = 2, C = 3, D = 4, E = 5, F = 6, G = 7, H = 8, I = 9, J = 10, K = 11, L = 12, M = 13, N = 14, O = 15, P = 16, Q = 17, R = 18, S = 19, T = 20, U = 21, V = 22, W = 23, X = 24, Y = 25, Z = 26

Now, let us examine the pattern for each of the given letter-clusters:

1. HLF:
Positional values: H = 8, L = 12, F = 6
First letter to second letter: $8+4=12$ (L)
Second letter to third letter: $12-6=6$ (F)

2. MQK:
Positional values: M = 13, Q = 17, K = 11
First letter to second letter: $13+4=17$ (Q)
Second letter to third letter: $17-6=11$ (K)

3. KOI:
Positional values: K = 11, O = 15, I = 9
First letter to second letter: $11+4=15$ (O)
Second letter to third letter: $15-6=9$ (I)

4. FJC:
Positional values: F = 6, J = 10, C = 3
First letter to second letter: $6+4=10$ (J)
Second letter to third letter: $10-7=3$ (C)

In the first three letter-clusters (HLF, MQK, KOI), the pattern followed is (+4, -6). However, in FJC, the pattern is (+4, -7). Therefore, FJC is the odd one out and does not belong to the group.