In the following groups: $I. -OAc$,$II. -OMe$,$III. -OSO_2Me$,$IV. -OSO_2CF_3$. The order of leaving group ability is:

Which of the following is most reactive towards ${S_N}^2$ reaction?

The rate of $S_{N}1$ reaction for the given compounds is:

Consider the reaction sequence shown below:
$Br-CH_2-CHO$ $\xrightarrow[\text{dry } HCl \text{ gas}]{\text{EtOH (excess)}} A$ $\xrightarrow{^tBuO^-K^+} B$
[Where $Et \Rightarrow -C_2H_5$,$^tBu \Rightarrow (CH_3)_3C^-$]
Identify the major products $A$ and $B$ formed respectively.

The reaction of $1$-chlorobutane with alcoholic $KOH$ yields .....

In $S_{N}2$ reaction,the carbon in the transition state is