no in case of 3 elements the set contains {a,b,c} only but here set contains {0,1,2,3,4,…..,49,50} so, total 51 elements and its powerset consists of {0length} {1length} {2length} …..till {all 51in one} . Moreover, you may do a mistake in counting 0 as 0length but actually its 1length so, 0length only contains ‘phi’ which is not directly connected with every other element but for the longest chain, we have to consider that phi is connected to all other elements in a single chain because phi is the subset of every set.
so, the answer should be 52.