Four letter clusters have been given, out of which three are alike in some manner and one is different. Select the odd letter cluster.

Logic: Each consecutive letters (+1, +1) in alphabet order.

Check each options:

Option A) QRS
Q +1 → R, R +1 → S

Option B) LKN
L −1 → K, K + 4 → N 

Option C) UVW
U +1 → V, V +1 → W 

Option D) HIJ
H +1 → I, I +1 → J 

 So, only LKN is not following the pattern of (+1, +1).

All options have consecutive letters (+1, +1), except LKN, which has irregular.

Thus, the correct option is: (b)