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 .

If $\operatorname{Ln}$ represents lanthanoid element find the general formula of lanthanoid hydroxide.

Identify the correct decreasing order of boiling points for different organic compounds from following.