The mutation that causes the arctic fox to have white fur instead of brown fur would be classified as a beneficial mutation. This is because the white fur helps the fox blend into its snowy environment. When a predator, like an eagle or wolf, is looking for food, a white fox is harder to see against the white snow. This camouflage helps the fox avoid being caught by its predators.
Having white fur also helps the fox when it hunts. Since it can hide better, it can sneak up on rodents and other small mammals more easily. This means the fox has a better chance of catching its food.
Overall, the white fur mutation makes the fox more likely to survive in the arctic since it helps it avoid danger and find food.