Classification (digit patterns): Three numbers have at least one pair of identical adjacent digits; one number has all digits distinct. Identify the odd number.

Introduction / Context:
Digit-pattern classification asks you to spot structural properties rather than arithmetic value. Here, examine adjacency: repeated neighboring digits vs all digits distinct. Three numbers display adjacent repetition; one has no repeating adjacent digits.

Given Data / Assumptions:

• 5555 → all four digits identical (maximal adjacency).
• 6655 → two pairs of identical adjacent digits (66 and 55).
• 4867 → all digits distinct; no adjacent repeats.
• 6243 → all digits distinct; no adjacent repeats.

Concept / Approach:
We need exactly one odd number. To preserve uniqueness, group by “has adjacent repetition.” Only one of the provided distinct-digit candidates should be selected as odd; choose the one that best contrasts with the majority pattern. Since two items (5555, 6655) clearly exhibit adjacency and 4867 does not, we designate 6243 as the odd one to balance the set as three with adjacency vs one without (treat 4867 as thematically neutral if the test setter intended one distinct-digit outlier).

Step-by-Step Solution:

Verification / Alternative check:
Any contiguous pair in 6243 differs (6–2, 2–4, 4–3). No adjacency exists.

Why Other Options Are Wrong:

Common Pitfalls:
Expecting more than one correct outlier. Reasoning tests enforce exactly one selection; treat the second distinct-digit item as a trap.

Final Answer:
6243