List the elements of the power set of the given set and give the cardinality of the power set.
a. ø

b. {a}

c. {a, b} 

d. {a, b, c}

For any set A, we denote by P(A) the collection of all subsets of A. For example, if A = {a, b, c, d}, then {a, b, d} ∈ P(A). The set P(A) is the power set of A.