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 letter-cluster pair 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)​

Checking the options;

Logic: 1st letter + 1 = 2nd letter, 3rd letter + 1 = 4th letter

a). PK - MJ

P + 1 → Q ≠ K, M + 1 → N ≠ J
So, this pair does not match the pattern.

b). NO - IJ

N + 1 → O, I + 1 → J
c). FG - AB

F + 1 → G, A + 1 → B

d). JK - EF

J + 1 → K, E + 1 → F

Thus, correct option is (a).