Which of the following propositions is logically equivalent to the proposition 'All frogs are amphibians'?

ANo amphibians are non-frogs

BNo frogs are non-amphibians ✓ Correct

CSome amphibians are frogs

DSome amphibians are not frogs

Correct answer: (B) No frogs are non-amphibians

Explanation

No frogs are non-amphibians states the same thing as All frogs are amphibians.

The given proposition is the universal affirmative All frogs are amphibians.

Obversion changes the quality and replaces the predicate with its complement.

Obverting All frogs are amphibians gives No frogs are non-amphibians.

Obversion is always truth-preserving, so the two are logically equivalent.

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