In this alphabet pattern reasoning question, select the odd group of letters from the following alternatives: ADG, HKN, ORU and BDF.

Introduction / Context:
This question tests your ability to recognize simple arithmetic progressions in the alphabet. You are given four groups of letters: ADG, HKN, ORU and BDF. In three groups, the letters progress forward with a constant step of plus three positions in the alphabet, while in one group the step is different. Your job is to find the group that does not follow the same step size and mark it as the odd one out.

Given Data / Assumptions:

• Letter groups: ADG, HKN, ORU and BDF.
• Alphabet positions: A = 1, B = 2, ..., Z = 26.
• We compare the differences between consecutive letters in each group.
• Three groups show a common pattern of +3, +3, while one group does not.

Concept / Approach:
We convert each letter to its numeric position and compute the difference from the first letter to the second and from the second to the third. If three groups show a difference of +3 each time and one group has a different difference, that group is the odd one out. This is a straightforward way to analyze alphabetic sequences in reasoning questions.

Step-by-Step Solution:
Step 1: Analyze ADG.A = 1, D = 4, G = 7. Differences: 1 to 4 = +3 and 4 to 7 = +3. Pattern: +3, +3.Step 2: Analyze HKN.H = 8, K = 11, N = 14. Differences: 8 to 11 = +3 and 11 to 14 = +3. Pattern: +3, +3.Step 3: Analyze ORU.O = 15, R = 18, U = 21. Differences: 15 to 18 = +3 and 18 to 21 = +3. Pattern: +3, +3.Step 4: Analyze BDF.B = 2, D = 4, F = 6. Differences: 2 to 4 = +2 and 4 to 6 = +2. Pattern: +2, +2, which is different from the +3, +3 pattern.Step 5: Identify the odd group.ADG, HKN and ORU all have equal jumps of three letters between each position, while BDF has jumps of two letters, so BDF is the odd group out.

Verification / Alternative check:
You can also verify visually by writing the alphabet and tracing each group. ADG jumps from A to D to G, always skipping two letters between selected ones, which corresponds to a step of three positions. HKN and ORU behave the same way. BDF, however, moves from B to D to F, skipping only one letter each time, which indicates a smaller step. This visual approach confirms that BDF does not fit the common structure of the other three groups.

Why Other Options Are Wrong:
ADG: Follows the pattern +3, +3 and is fully consistent with HKN and ORU.
HKN: Shows the same step size of three letters between positions.
ORU: Continues the same type of forward progression and belongs to the same pattern family.

Common Pitfalls:
Students sometimes focus only on whether groups are increasing or decreasing and overlook the actual step size. In this question, all groups are increasing, so you need to examine the spacing carefully. Always measure the exact difference in positions when solving alphabet sequence problems to avoid missing such subtle but important details.

Final Answer:
The odd group of letters is BDF, because it advances by two alphabet positions at each step, while ADG, HKN and ORU each advance by three positions at every step.