Odd-one-out (lexical category focus): Select the word that is different from the other three based primarily on its form as an English lexical item (spelling/wordform), not on generic “electronic device” similarities.

Introduction / Context:
This classification question asks you to identify the odd item by focusing on each option’s lexical form (i.e., how the word is written in English), rather than loosely grouping them as “devices.” Paying attention to spelling, morphology, and part-of-speech patterns is a reliable way to resolve otherwise ambiguous odd-one-out sets.

Given Data / Assumptions:

• Options: AC, Calculator, Cooler, Computer.
• We prioritize lexical form over broad functional overlap.
• No additional domain constraints (brand, power source, etc.) are provided.

Concept / Approach:
Look for a property that is both unique and unambiguous. “AC” is an initialism (two uppercase letters), whereas “Calculator,” “Cooler,” and “Computer” are standard English common nouns written in full lowercase (when not sentence-initial), with typical suffixes like -or, -er, and -er.

Step-by-Step Solution:

Verification / Alternative check:
Functional categories are ambiguous here (e.g., “Cooler” vs “AC” as cooling devices, “Computer”/“Calculator” as computing devices) because they split 2–2. Lexical form, however, cleanly separates one item (“AC”) from the other three.

Why Other Options Are Wrong:
“Calculator,” “Cooler,” and “Computer” share the property of being standard, fully spelled common nouns. None is an initialism.

Common Pitfalls:
Overfitting a “device-type” rule leads to ties (2 cooling devices vs 2 computing devices). The prompt allows us to use form when semantics do not yield a single outlier.

Final Answer:
AC