1. The problem asks for the number of elements in the power set of a set with $n$ elements. 2. The power set of a set is the set of all possible subsets of the original set. 3. Each element can either be in or out of a subset, so for each of the $n$ elements, there are 2 choices. 4. Therefore, the total number of subsets is $$2^n$$. 5. Hence, the power set has $2^n$ elements. The correct answer is b. $2^n$.