b
\(3 Pb \left( NO _{3}\right)_{2}+ Cr _{2}\left( SO _{4}\right)_{3} \rightarrow 3 PbSO _{4}+2 Cr \left( NO _{3}\right)_{3}\)

\(35\, ml \quad 20\, ml\)

\(0.15\, M \quad 0.12\, M\)

\(5.25\, m \cdot mol =2.4\, m \cdot mol \quad 5.25 \,m \cdot mol\)

\(=5.25 \times 10^{-3} \,mol\)

therefore moles of \(PbSO _{4}\) formed \(=5.25 \times 10^{-3}\) \(=525 \times 10^{-5}\)