(i) Number of elements in given set = 1
Number of subsets of given set = 21 = 2
\ Subsets of given set are ϕ, {a}.
(ii) Number of elements in given set = 2
Number of subsets of given set = 22 = 4
\ Subsets of given set are ϕ, {a}, {b}, {a, b}.
(iii) Number of elements in given set = 3
Number of subsets of given set = 23 = 8
\ Subsets of given set are ϕ, {1}, {2}, {3}, {1, 2}, {2, 3}, {1, 3}, {1, 2, 3}.
(iv) Number of elements in given set = 0
Number of subsets of given set = 20 = 1
\ Subset of given set is ϕ.