The mutation that makes the arctic fox have white fur instead of brown can be classified as a beneficial mutation. This is because the arctic fox lives in a snowy environment, and having white fur helps it blend in with the snow. When the fox is camouflaged, it is less likely to be seen by its predators like eagles, wolves, and polar bears. This camouflage also helps it to sneak up on its prey, such as rodents, making it easier to hunt them.
So, having white fur would make the fox more likely to survive in its snowy habitat. If it had brown fur, it would stand out against the white snow, making it easier for predators to spot it and harder for it to catch food. Overall, this mutation helps the fox adapt better to its environment, which is a really good thing for its survival!