Which scenario is an example of Müllerian mimicry?

Müllerian mimicry occurs when two or more unpalatable or harmful species evolve to resemble one another, which reinforces the avoidance behavior of predators. This mutual resemblance benefits all species involved, as predators learn more quickly to avoid individuals that share similar warning coloration or other characteristics.

In the context of the choices provided, the scenario involving the viceroy butterfly mimicking the monarch butterfly fits this definition. Both the viceroy and monarch are unpalatable to predators, and their similar appearances serve to enhance predator avoidance of both species. This is an example of Müllerian mimicry because both species are harmful, leading to a mutually beneficial relationship in terms of predator deterrence.

The other options do not conform to this concept of mutual harmfulness and mimicry, as harmless species imitating harmful ones would represent Batesian mimicry rather than Müllerian mimicry, while camouflage employed by predators and plant resemblance does not involve the collaboration between harmful species.