2. a) Æ = {Æ} False, as {Æ} has one element, whereas Æ has zero elements.
b) A È Æ = A True, as Æ has no elements, so the union of any set with Æ gives just the original set.
c) A Ç Ac = Æ True, by the definition of complement, a set and its complement have no elements in common.
d) A È Ac = Æ False, this union will give the universal set.
e) A Ç Æ = Æ True, as Æ has no elements.
f) (A - B) Ç B = Æ True, as (A - B) has no elements in common with B.
g) {a, b, c} and {d, e} are disjoint sets. True, as the two sets have no elements in common.
h) {1, 2}, {5, 7, 9} and {3, 4, 5} are mutually disjoint sets. False, as the sets {5, 7, 9} and {3, 4, 5} have the element 5 in common.