1. compared to the desert fennec, you might expect the arctic fox to have

Smaller ears, more dense and light coloured fur.

Explanation:

Smaller ears means that the surface area of the animal is decreased.

Less surface area = Less heat loss

Denser fur is self-explanatory. If the animal has more fur, that means that it will have better insulation. The light colouration of the fur is mainly for camouflage but it can also serve as a way of insulating/preventing heat from escaping.

well, i believe that the answer is 2. : 3

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.