When $but-3-en-2-ol$ reacts with aqueous $HBr$,which of the following products is obtained?

In which of the following compounds does the carbon atom attached to the halogen possess $sp^2$ hybridization?

Give the chemical reactions for the following conversions:
$(1)$ $m$-nitrobenzoic acid from toluene
$(2)$ $m$-chloronitrobenzene from benzene
$(3)$ $n$-propyl bromide from $1, 2$-dibromopropane

The end product of the given reaction is:

Identify the major product formed from the following reaction sequence:

The correct order of increasing reactivity of $C-X$ bond towards nucleophile in the following compounds is:
$I$: Chlorobenzene (or aryl halide)
$II$: $2,4$-Dinitrochlorobenzene
$III$: $(CH_3)_3C-X$ ($3^o$ alkyl halide)
$IV$: $(CH_3)_2CH-X$ ($2^o$ alkyl halide)