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 is the one that does not belong to that group?
(NOTE: The odd man out is not based on the number of consonants/vowels or their position in the letter cluster.)

The correct option is LN - CE.

To understand why LN - CE is the odd one out, let us analyze the pattern governing the relationship between the two letter-clusters in each pair based on their positions in the English alphabetical order.

First, let us list the positional values of 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 differences between corresponding letters in each pair of clusters:

Analyzing Pair 2: QS - IK
• First letters: Q (17) and I (9). The difference is:
$17-9=8$
��� Second letters: S (19) and K (11). The difference is:
$19-11=8$
Both letters in the first cluster are shifted backwards by 8 positions to get the second cluster.

Analyzing Pair 3: XZ - PR
• First letters: X (24) and P (16). The difference is:
$24-16=8$
• Second letters: Z (26) and R (18). The difference is:
$26-18=8$
Both letters in the first cluster are shifted backwards by 8 positions to get the second cluster.

Analyzing Pair 4: SU - KM
• First letters: S (19) and K (11). The difference is:
$19-11=8$
• Second letters: U (21) and M (13). The difference is:
$21-13=8$
Both letters in the first cluster are shifted backwards by 8 positions to get the second cluster.

Analyzing Pair 1 (Correct Option): LN - CE
• First letters: L (12) and C (3). The difference is:
$12-3=9$
• Second letters: N (14) and E (5). The difference is:
$14-5=9$
Here, the difference is 9 instead of 8.

Thus, while all other options follow a constant difference of 8 positions between corresponding letters, the pair LN - CE deviates from this rule with a difference of 9, making it the odd one out.