Which of the following reagents is used to prepare alkyl isocyanides from alkyl halides $(RX)$?

The major product of the following reaction is:
$Ph-CH(CH_3)-CH(Br)-CH_2-CH_2-Br \xrightarrow{KOH \text{ (alc, excess)}, \Delta} ?$

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.

Which among the following compounds undergoes $SN^2$ reaction most rapidly?

$(R)-2-$octyl tosylate is solvolyzed in water under ideal $S_{N}1$ conditions. The product$(s)$ will be

The decreasing order of reactivity towards dehydrohalogenation $(E_1)$ reaction of the following compounds is:
$(A)$ $CH_3CH_2CH_2CH_2Cl$
$(B)$ $CH_2=CHCH_2CH_2Cl$
$(C)$ $CH_3CH_2CHClCH_3$
$(D)$ $CH_2=CHCHClCH_3$