Classification (whole–part vs co-hyponyms): Three pairs denote a whole–part relationship; one pair denotes two coordinate types rather than part and whole. Identify the odd pair.

Introduction / Context:
Semantic relation problems frequently contrast whole–part relations with other lexical relations such as co hyponymy (sibling categories under a common supertype). Recognizing these distinctions is essential for accurate classification. In this item, most pairs encode a whole that contains a part, while one pair lists two coordinate items under the same higher category rather than a part and its containing whole.

Given Data / Assumptions:

• Pairs: Tree : Stem, Face : Eye, Chair : Sofa, Plant : Flower.
• “Whole–part” means the second term is a constituent component of the first (for example, eye is part of a face).
• “Co hyponyms” are two different kinds of the same broader category (for example, chair and sofa are both types of furniture).

Concept / Approach:
Test each pair by asking whether the second term can be said to be included as a component within the first. If yes, it is a whole–part pair. If the two terms are merely siblings under a broader type without inclusion, the pair is not whole–part and becomes the exception.

Step-by-Step Solution:

Verification / Alternative check:
Attempt the phrase “X has a Y.” “A face has an eye,” “A tree has a stem,” and “A plant has a flower” are natural. “A chair has a sofa” is not natural, confirming that it is not a whole–part relation.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing co hyponyms with part–whole pairs due to frequent co occurrence in the same domain. Always test inclusion rather than association.

Final Answer:
Chair : Sofa