In the letter sequences ACEG, BDFG, JLNP and SUWY, identify the odd sequence based on equal spacing of letters.

Introduction / Context:
Letter sequence odd one out questions typically rely on a constant step or gap between consecutive letters in the alphabet. Three sequences maintain the same gap throughout, while one sequence contains a break in that pattern. In this problem, we are given four sequences of four letters each and asked to detect the sequence that does not maintain a consistent step size between letters.

Given Data / Assumptions:
The sequences are ACEG, BDFG, JLNP and SUWY. We map letters to positions: A = 1, B = 2, ..., Z = 26. We examine the difference between consecutive letters in each sequence.

Concept / Approach:
The central concept is constant spacing. In a well structured sequence, each pair of consecutive letters has the same alphabetical gap, for example a gap of 2: A, C, E, G. To solve the question, we compute the difference in positions between each pair of neighboring letters in every sequence. If three sequences maintain a constant difference of 2 and one sequence deviates from this, the deviating one is the odd sequence.

Step-by-Step Solution:
Step 1: For ACEG, positions are A = 1, C = 3, E = 5, G = 7. Differences are 3 - 1 = 2, 5 - 3 = 2 and 7 - 5 = 2. So ACEG has a constant gap of 2. Step 2: For BDFG, positions are B = 2, D = 4, F = 6, G = 7. Differences are 4 - 2 = 2, 6 - 4 = 2 and 7 - 6 = 1. The last gap is 1, not 2, so the pattern breaks. Step 3: For JLNP, positions are J = 10, L = 12, N = 14, P = 16. Differences are 12 - 10 = 2, 14 - 12 = 2 and 16 - 14 = 2. Constant gap of 2 is maintained. Step 4: For SUWY, positions are S = 19, U = 21, W = 23, Y = 25. Differences are 21 - 19 = 2, 23 - 21 = 2 and 25 - 23 = 2. Again we have a constant difference of 2. Step 5: ACEG, JLNP and SUWY have a uniform spacing of 2, while BDFG does not, so BDFG is the odd sequence.

Verification / Alternative check:
By simply writing the sequences in alphabet order with indices, we can visually inspect the jumps and confirm that only BDFG has a smaller final jump. No other straightforward rule such as reverse order or mixed gaps fits all sequences as neatly as the constant gap rule. Therefore, the constant step pattern is the intended logic for this question.

Why Other Options Are Wrong:
ACEG is not the odd sequence because it follows the 2 step pattern completely. JLNP is not the odd sequence because it also maintains a constant gap of 2 between all letters. SUWY is not the odd sequence because it continues the same step size of 2 throughout. BDFG is different because its last jump from F to G is only 1 step, breaking the uniform spacing.

Common Pitfalls:
Some candidates may only check the first two gaps in each sequence and overlook a later break in the pattern, as happens in BDFG. Others may try to find meaning in the sequences as abbreviations rather than as abstract letter progressions. To avoid mistakes, always compute all the gaps in every sequence and confirm that the pattern holds from start to end.

Final Answer:
The letter sequence that does not maintain a constant gap of 2 and is therefore the odd one out is BDFG.