In this letter-pattern reasoning question, select the odd group of letters from the following: ECA, GIK, QOM, WUS.

Introduction / Context:
This question tests your ability to recognize patterns in groups of letters. The options are ECA, GIK, QOM and WUS. You must identify which group does not follow the same directional rule as the others. These groups involve letters taken from the alphabet with either forward or backward movement, so studying their order is crucial.

Given Data / Assumptions:

• Letter groups: ECA, GIK, QOM, WUS.
• We work with alphabetical positions: A = 1, B = 2, ..., Z = 26.
• Three groups follow a descending pattern with equal steps.
• One group follows an ascending pattern and is therefore the odd one out.

Concept / Approach:
The best approach is to examine how letters move within each group. If in most groups the letters decrease by a fixed step from left to right, while in one group they increase, that increasing group is the odd one out. We do not need any semantic meaning from the letters, only their order and spacing in the alphabet.

Step-by-Step Solution:
Step 1: Analyze ECA.E = 5, C = 3, A = 1. The pattern is 5, 3, 1, which is a descending sequence with a step of -2 each time.Step 2: Analyze QOM.Q = 17, O = 15, M = 13. The pattern is 17, 15, 13, again a descending sequence with a step of -2.Step 3: Analyze WUS.W = 23, U = 21, S = 19. This is 23, 21, 19, yet another descending sequence with step -2.Step 4: Analyze GIK.G = 7, I = 9, K = 11. This pattern is 7, 9, 11, which is an ascending sequence with a step of +2.Step 5: Compare the four groups.ECA, QOM and WUS all move backward through the alphabet in steps of -2, whereas GIK moves forward in steps of +2, making it the odd group.

Verification / Alternative check:
If you write the alphabet in order and mark the letters of each group, you will see that ECA, QOM and WUS all go from right to left when read across the alphabet, while GIK moves left to right. Visualizing them as arrows across the alphabet line makes the difference obvious: three arrows point backward, and one arrow points forward.

Why Other Options Are Wrong:
ECA: Shows a clear backward movement with equal steps of -2 and matches the structure of QOM and WUS.
QOM: Another backward run with step -2, consistent with the majority pattern.
WUS: Again a backward sequence with step -2, so it belongs with ECA and QOM.

Common Pitfalls:
Candidates sometimes only look at the first and last letters and ignore the middle letter, which can hide the step size pattern. Others may try to interpret the groups as abbreviations or codes. For letter series questions, always translate letters into positions and check whether the sequence is increasing or decreasing and by how much. This avoids confusion and quickly reveals which group is different.

Final Answer:
The odd group of letters is GIK, because it is arranged in ascending order with step +2, while ECA, QOM and WUS are arranged in descending order with step -2.