\(s_2 = [Pb^{+2}] [S^{-2}]\)
\(3.4 \times 10^{-28} = [0.001] [S^{-2}]\)
\([{S^{ - 2}}] = \frac{{{K_{sp}}}}{{[P{b^{ + 2}}]}} = \frac{{3.4 \times {{10}^{ - 28}}}}{{{{10}^{ - 3}}}} = 3.4 \times {10^{ - 25}} = 3.4 \times {10^{ - 25}}\)