Three of the following four are alike in a certain way and thus form a group. Which is the one that 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 KMP.

To determine which letter cluster does not belong to the group, let us analyze the pattern of positional values of the alphabet for each given cluster:

1. BEH:
B = 2
E = 5 (2 + 3 = 5)
H = 8 (5 + 3 = 8)
Pattern: Difference of +3 between consecutive letters (+3, +3).

2. RUX:
R = 18
U = 21 (18 + 3 = 21)
X = 24 (21 + 3 = 24)
Pattern: Difference of +3 between consecutive letters (+3, +3).

3. NQT:
N = 14
Q = 17 (14 + 3 = 17)
T = 20 (17 + 3 = 20)
Pattern: Difference of +3 between consecutive letters (+3, +3).

4. KMP:
K = 11
M = 13 (11 + 2 = 13)
P = 16 (13 + 3 = 16)
Pattern: Difference is (+2, +3), which breaks the (+3, +3) rule followed by the other three clusters.

Hence, KMP is the odd one out and does not belong to the group.