Which of the following compounds has the most acidic hydrogen?

Explain the following with an example.
$(i)$ Kolbe's reaction.
$(ii)$ Reimer-Tiemann reaction.
$(iii)$ Williamson ether synthesis.
$(iv)$ Unsymmetrical ether.

The increasing order of boiling points of the following is:

Molecule	Label
$CH_3-O-CH_3$	$I$
$CH_3CHO$	$II$
$CH_3CH_2CH_3$	$III$
$CH_3CH_2OH$	$IV$

Match the columns:

Column-$I$	Column-$II$
$A$. Methanol	$p$. Conversion of phenol to salicylic acid
$B$. Kolbe's reaction	$q$. Wood spirit
$C$. Williamson's reaction	$r$. Vapours are passed over heated copper at $573 \ K$
$D$. Conversion of $2^\circ$ alcohol to ketone	$s$. Reaction of alkyl halide with sodium alkoxide

Match each of the compounds given in Column $I$ with the reaction$(s)$ that they can undergo,given in Column $II$.
| Column $I$ | Column $II$ |
| :--- | :--- |
| $(A)$ $3-$bromobenzofuran derivative | $(p)$ Nucleophilic substitution |
| $(B)$ Benzyl alcohol | $(q)$ Elimination |
| $(C)$ Salicylaldehyde | $(r)$ Nucleophilic addition |
| $(D)$ $1-$bromo$-2-$nitrobenzene | $(s)$ Esterification with acetic anhydride |
| | $(t)$ Dehydrogenation |

In which one of the following conversions is phosphorus pentachloride $(PCl_5)$ used as a reagent?