Since, set A contains n elements. So, it has 2n subsets.∴ Set P can be chosen in 2n ways, similarly set Q can be chosen in 2n ways.∴P and Q can be chosen in (2n)(2n)=4n ways.Suppose, P contains r elements, where r varies from 0 to n. Then, P can be chosen in nCr​ ways, for 0 to be disjoint from A, it should be chosen from the set of all subsets of set consisting of remaining (n−r) elements. This can be done in 2n−r ways.∴P and Q can be chosen in nCr​⋅2n−r ways.But, r can vary from 0 to n.∴ Total number of disjoint sets P and Q=∑r=0n​Cr​2n−r=(1+2)n=3nHence, required probability =4n3n​=(43​)n