Which of the following chloro-compounds shows complete inversion of configuration during a reaction?

Pure $CHCl_3$ and pure $CHI_3$ can be distinguished by which of the following?

Which one of the following is more reactive towards $S_{N}2$ reaction?

Among the following,the most reactive towards alcoholic $KOH$ is:

The reactivity order of the following molecules towards $S_N1$ reaction is:
$(I)$ Allyl chloride
$(II)$ Chlorobenzene
$(III)$ Ethyl chloride

Explain why:
$(i)$ the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride?
$(ii)$ alkyl halides,though polar,are immiscible with water?
$(iii)$ Grignard reagents should be prepared under anhydrous conditions?