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Which of the following is true?i The order of reactivity in $\mathrm {S_N2}$ is $\mathrm {CH_3X>1^°>2^°>3^°}$ii The order of reactivity in $\mathrm {E_2}$ is $\mathrm {CH_3X >1^°>2^° ~ 3^°}$iii Strong base favors the $\mathrm {E_2}$ and $\mathrm {S_N2}$ reactions.iv. More polar solvent favors $\mathrm {S_N1}$ reaction but less polar solvent $\mathrm {E_1}$ reaction.