Most reactive compound toward $S_N1$ is

Arrange the compounds of each set in order of reactivity towards $S_{N}2$ displacement:
$(i)$ $2-Bromo-2-methylbutane$,$1-Bromopentane$,$2-Bromopentane$
$(ii)$ $1-Bromo-3-methylbutane$,$2-Bromo-2-methylbutane$,$2-Bromo-3-methylbutane$
$(iii)$ $1-Bromobutane$,$1-Bromo-2,2-dimethylpropane$,$1-Bromo-2-methylbutane$,$1-Bromo-3-methylbutane$.

What is retention and inversion of configuration? Explain with suitable examples.

Decreasing the concentration of an electrophile (substrate) in a typical $S_N2$ reaction by a factor of $3$ will cause the reaction rate to

Identify reagent $B$ in the following reaction: $R - X \xrightarrow{B} \text{Nitroalkane}$

$Cl-CH_2-C(CH_3)_2-CH_2-CH_2-Cl + I^- \xrightarrow[DMF]{} \text{product}$; The major product of this reaction is: