Classification – Four-letter codes (step pattern): in three codes the letter steps alternate +a, −(a−3), +(a−6) (strict descending magnitudes); one code breaks this alternation with a zero step. Find the odd one out. Options: DWFU, EVHS, HSKP, KQNN.

Introduction / Context:
Alphabet-code classification frequently uses alternating forward/backward steps with steadily shrinking magnitudes. The outlier often breaks either the sign alternation or the monotone decrease of step sizes.

Given Data / Assumptions:

• Compute differences letter-to-letter using A=1 … Z=26.
• DWFU → +19, −17, +15 (magnitudes 19→17→15, alt signs).
• EVHS → +17, −14, +11 (17→14→11, alt signs).
• HSKP → +11, −8, +5 (11→8→5, alt signs).
• KQNN → +6, −3, 0 (third step is zero; alt pattern breaks).

Concept / Approach:
Identify the majority pattern: signs alternate +, −, + with strictly decreasing magnitudes by 3 (or close), never reaching zero. The code with a zero step (no movement) is the misfit.

Step-by-Step Solution:
Confirm alternation and decreasing sizes for DWFU, EVHS, HSKP.Observe KQNN third step 0 (N→N), violating the alternation and decrease rule.

Verification / Alternative check:
Even if minor variance in the amount exists (e.g., 19→17→15 vs 17→14→11), the structural +/−/+ with strictly positive steps holds for three codes, but not for KQNN.

Why Other Options Are Wrong:
DWFU/EVHS/HSKP: Each preserves the alternating sign and nonzero descending step magnitudes.

Common Pitfalls:
Ignoring the zero step; a repeated letter indicates no movement and thus a pattern break.

Final Answer:
KQNN