Which from following mixtures obeys Raoult's law?

In a first order reaction concentration of reactant decreases from 20 milli $\mathrm{mol} \mathrm{dm}^{-3}$ to 8 milli $\mathrm{mol} \mathrm{dm}^{-}$ in 40 minutes, find rate constant of reaction?

Identify the reagent $R$ used in following reaction.

Ketone $$\buildrel R \over \longrightarrow$$ semi carbazone

Which from following polymers needs peroxide as initiator for preparation?