Based on the English alphabetical order, three of the following four letter-clusters pairs are alike in a certain way and thus form a group. Which pair does not belong to that group?

(Note: The odd one out is not based on the number of consonants/vowels or their positions in the letter cluster.)

Q → S: +2 positions forward.

V → X: +2 positions forward.

Pattern: Both letters in the first pair move +2 positions forward to form the second pair.

K → M: +2 positions forward.

P → R: +2 positions forward.

Pattern: Both letters in the first pair move +2 positions forward to form the second pair.

A → C: +2 positions forward.

D → G: +3 positions forward.

Pattern: The two letters in the pair move +2 and +3, which differs from the consistent +2 seen in the earlier options.

B → D: +2 positions forward.

G → I: +2 positions forward.

Pattern: Both letters in the first pair move +2 positions forward to form the second pair.

Conclusion: The pattern in C. AD - CG is inconsistent because the letters move by +2 and +3, whereas in the other options, both letters move consistently by +2.

Final Answer: option (c). AD - CG