What is the denotation of a "snake"?

A denotation is the literal meaning of something.
A snake is not an amphibian. Amphibians are animals, mostly four-legged vertebrates that do not have amniotic eggs but live on both land and water. Examples are toads and frogs. Snakes cannot live in water. They can only survive on land.

A snake is a reptile. Reptile is a class of cold-blooded vertebrates. They usually move on the belly or by a means of short or small legs.

Option B is also wrong because it explains the connotation of a snake, a snake is used to describe a liar, cheater or fraud, someone that behaves nice but turn out to be a wicked person which doesn't explain the denotation of a snake.