(b) Reflexiveness: since the population of any city is certainly not greater than its own population.
Anti-symmetry: Assume that there exist . Then, the population of town x is not greater than the population of town y, but the population of town y is also not greater than the population of town x. If you may, this gives us that , so the populations of x and y are equal, however this certainly doesn't guarantee us that they are the same city, seeing as two cities may have the same population. Hence, there is no anti-symmetry.
Can you do transitivity?