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 letter-cluster is not based on the number of consonants/vowels or their position in the letter-cluster.)

​Logic: first letter to second letter -3, first letter to third letter +2

Q - 3 → N

Q + 2 → S $$\not=$$ R

T - 3 → Q

T + 2 → V

N - 3 → K

N + 2 → P

K - 3 → H

K + 2 → M

So, QNR the odd one out.

Thus, the correct option is: (a)