Odd one out.

Concept:

In an 'odd one out' letter-series question, three of the four groups are built using the same transformation rule (often a constant alphabetical shift), while exactly one group breaks that rule. The task is to identify the shared rule from the groups that fit it, then test every group against it to isolate the one that does not.

Application:

Convert each letter to its alphabet position (A = 1, B = 2, ..., Z = 26) and check the difference between consecutive letters in every group.

• IGEC: I(9) → G(7) → E(5) → C(3) — every step is −2.

• PNLJ: P(16) → N(14) → L(12) → J(10) — every step is −2.

• SQOM: S(19) → Q(17) → O(15) → M(13) — every step is −2.

• TRQO: T(20) → R(18) → Q(17) → O(15) — the first step is −2, but the second step (R → Q) is only −1 instead of −2, before the third step returns to −2.

Cross-check:

IGEC, PNLJ, and SQOM each maintain a constant −2 shift across all three steps, confirming they follow the same rule. TRQO is the only group where one step deviates from −2 (R → Q is −1), so it is the group that breaks the shared pattern.

Conclusion:

TRQO is the odd one out.