In the following question, select the odd letters from the given alternatives: IKM, OQS, GEC and UWY. In three of these letter groups, the letters are arranged in increasing alphabetical order with a constant step of +2 between consecutive letters, while in one group the letters are arranged in decreasing order. Which group of letters is the odd one out?

Introduction / Context:
This is a letter series odd one out question from the reasoning section. You are given four three-letter groups and must determine which group does not follow the same alphabetical pattern as the others. Three sequences go forward in the alphabet with equal steps, while one sequence goes backward, making it the odd one out.

Given Data / Assumptions:

• Letter groups: IKM, OQS, GEC, UWY.
• Alphabet positions: A = 1, B = 2, ..., Z = 26.
• We will compute the position of each letter and examine whether the sequences are ascending or descending.
• We expect three groups to be ascending with a constant step and one to be descending.

Concept / Approach:
The approach is to:

• Convert letters to their numerical positions.
• Check the difference between consecutive letters.
• Note whether the letters are increasing or decreasing, and by how much.

In three groups, the letters should increase by a fixed step of +2. In the odd group, the letters move in the opposite direction.

Step-by-Step Solution:
Step 1: For IKM: I = 9, K = 11, M = 13. Differences: K - I = 11 - 9 = 2, M - K = 13 - 11 = 2. This is an increasing sequence with a constant step of +2. Step 2: For OQS: O = 15, Q = 17, S = 19. Differences: Q - O = 17 - 15 = 2, S - Q = 19 - 17 = 2. Again, an increasing sequence with a step of +2. Step 3: For UWY: U = 21, W = 23, Y = 25. Differences: W - U = 23 - 21 = 2, Y - W = 25 - 23 = 2. Once more, an increasing sequence with a step of +2. Step 4: For GEC: G = 7, E = 5, C = 3. Differences: E - G = 5 - 7 = -2, C - E = 3 - 5 = -2. Here, the sequence is decreasing with a step of -2. Step 5: While IKM, OQS and UWY are ascending sequences with equal positive steps, GEC is a descending sequence with equal negative steps, making it different from the others.

Verification / Alternative check:
An alternative quick check is to recite the alphabet and see whether the letters in each group appear in forward order or reverse order: IKM: I, J, K, L, M – forward. OQS: O, P, Q, R, S – forward. UWY: U, V, W, X, Y – forward. GEC: G, F, E, D, C – backward. Only GEC clearly moves backwards in the alphabet, confirming it as the odd one out.

Why Other Options Are Wrong:
IKM is not odd because it is an increasing sequence with constant steps of +2. OQS is not odd because it also increases with steps of +2 between letters. UWY is not odd because it similarly follows the +2, +2 forward pattern. GEC alone moves backward in steps of -2, differing from the forward sequences of the others.

Common Pitfalls:
A common mistake is to focus only on the absolute size of the step and ignore the direction (forward or backward). While the step magnitude is 2 in all groups, the direction is crucial for this question. Another pitfall is misremembering alphabet positions or miscounting, so always check letter order carefully.

Final Answer:
The letter group that moves in the reverse direction and is therefore the odd one out is GEC.