$35\, ml \quad 20\, ml$
$0.15\, M \quad 0.12\, M$
$5.25\, m \cdot mol =2.4\, m \cdot mol \quad 5.25 \,m \cdot mol$
$=5.25 \times 10^{-3} \,mol$
therefore moles of $PbSO _{4}$ formed $=5.25 \times 10^{-3}$ $=525 \times 10^{-5}$
$^{200}X \,:\, 90\%$ $^{199}X\, :\, 8.0\%$ $^{202}X\, :\, 2.0\%$