2. i) For all positive integers a, a | a, since a = a · 1, so the "divides" relation is reflexive.
ii) For all positive integers a and b, if a | b, then b = a · k for some integer k. However, this does not imply that b | a, (for instance, let a = 2 and b = 4), so the "divides" relation is not symmetric.
iii) For all positive integers a, b and c, if a | b and b | c, then b = a · p for some integer p and c = b · q for some integer q. Hence c = (a · p) · q = a · r for some integer r, and so a | c. Therefore, the "divides" relation is transitive.