What is the difference in molar masses of Undecane and Decane?

Which of the following is effectively used instead of DDT?

A compound of Xe and F is found to have atomic ratio $\mathrm{Xe}: \mathrm{F}$ as $0.4: 2.4$, Find the oxidation number of Xe ?

A weak monoacidic base dissociates to $1.5 \%$ in 0.001 M solution at 298 K . Calculate the dissociation constant of weak base.