In the letter sequences AEIM, BFJN, CGKO and FDKN, find the odd sequence based on regular jumps in the alphabet.

Introduction / Context:
This is an alphabet series odd one out question, where each option is a group of four letters. Most groups are constructed using a regular jump in the alphabet. You have to identify the one group that does not follow the same consistent step pattern. Such problems test your ability to convert letters to numbers and detect arithmetic patterns quickly.

Given Data / Assumptions:
The letter groups given are AEIM, BFJN, CGKO and FDKN. Each group contains four letters arranged in a specific order. We use the standard mapping A = 1, B = 2, C = 3, and so on up to Z = 26. We assume that the pattern, if any, is formed by equal increments in alphabetical positions.

Concept / Approach:
A common construction in alphabet series questions is to take a starting letter and then add a fixed number of positions repeatedly to get the next letters. Here we look at each group and check whether consecutive letters are separated by the same fixed jump. If three groups show a step of plus 4 between consecutive letters and one group does not, that inconsistent group is the odd one out. Converting letters to numbers allows us to see this clearly.

Step-by-Step Solution:
Step 1: For AEIM, the letters are A, E, I and M. Their positions are 1, 5, 9 and 13. The differences are 5 - 1 = 4, 9 - 5 = 4 and 13 - 9 = 4. So this group uses a constant step of +4. Step 2: For BFJN, the letters are B, F, J and N. Their positions are 2, 6, 10 and 14. The differences are 6 - 2 = 4, 10 - 6 = 4 and 14 - 10 = 4. This group also uses a constant step of +4. Step 3: For CGKO, the letters are C, G, K and O. Their positions are 3, 7, 11 and 15. The differences are 7 - 3 = 4, 11 - 7 = 4 and 15 - 11 = 4, again a constant step of +4. Step 4: For FDKN, the letters are F, D, K and N. Their positions are 6, 4, 11 and 14. The moves are 4 - 6 = -2, then 11 - 4 = 7 and 14 - 11 = 3. These jumps are -2, +7 and +3, which do not match the regular +4 pattern. Step 5: Since AEIM, BFJN and CGKO all follow the same simple rule of adding four positions each time, and FDKN does not, FDKN is the odd sequence.

Verification / Alternative check:
As a quick check, you can write the alphabet in a row and verify that in AEIM you skip three letters between each pair, which corresponds to a four step move. The same skipping pattern appears in BFJN and CGKO, but in FDKN the letters jump backward and forward irregularly, confirming that it is different. No simple arithmetic adjustment can turn the sequence of FDKN into a constant step pattern similar to the other three groups.

Why Other Options Are Wrong:
AEIM is not the odd group because it consistently uses a +4 step between letters. BFJN is not the odd group because it also follows the same +4 step pattern. CGKO is not the odd group because it again uses a constant jump of four positions in the alphabet. FDKN is the odd group because its sequence of letter positions does not follow a constant step and instead has irregular jumps.

Common Pitfalls:
One common mistake is to look for a pattern based on the shapes of letters rather than their positions in the alphabet. Another pitfall is to notice only one or two of the jumps in a group and conclude a pattern without checking all differences carefully. To solve such questions reliably, always convert letters to numbers and compute each step explicitly before deciding which sequence breaks the rule.

Final Answer:
The letter sequence that does not follow the constant +4 alphabetical step and is therefore the odd one out is FDKN.