a
Let \(V.P.\) of pure \(A\) be \(P _{ A }^0\)

Let \(V.P\) of pure \(B\) be \(P _B^0\)

When \(X _{ A }=0.7 \& X _{ B }=0.3\) \(P _{ s }=350\)

\(\Rightarrow P _{ A }^0 \times 0.7+ P _{ B }^0 \times 0.3=350\)

When \(X _{ A }=0.2 \& X _{ B }=0.8\)

\(P _{ s }=410\)

\(\Rightarrow P _{ A }^0 \times 0.2+ P _{ B }^0 \times 0.8=410\)

Solving \((i)\) and \((ii)\) \(P _{ A }^0=314\,mm\,Hg\)

\(P _{ B }^0=434\,mm\,Hg\)

\(=(314)\)