The correct answer Is (C).
Since, let \(A\) and \(B\) be such sets, i.e., \(n(A)=m, n(B)=n\)
So \(n(P(A))=2^{m}, n(P(B))=2^{n}\)
Thus \(n(P(A))-n(P(B))=56\), i.e., \(2^{m}-2^{n}=56\)
\(=2^{n}\left(2^{m-n}-1\right)=2^{3} 7\)
\(=n=3,2^{m-n}-1=7\)
\(=m=6\)