Which from following cations will form most stable complex with same ligand?

Which is NOT correct regarding stock notation?

Calculate the time in seconds required to reduce the concentration of reactant to half of initial concentration for first order reaction if rate constant is $1.386 \times 10^{-3} \mathrm{~s}^{-1}$.

The solubility product of $\mathrm{PbI}_2$ is $1.08 \times 10^{-7}$.

Calculate its solubility in $\mathrm{mol} \mathrm{dm}^{-3}$ at 298 K .