Which reagent is used to distinguish between acetaldehyde and acetophenone?

The reaction shown in the image proceeds via which mechanism?

When liquid $A$ is treated with a freshly prepared ammoniacal silver nitrate solution,it gives a bright silver mirror. The liquid forms a white crystalline solid on treatment with sodium hydrogensulphite. Liquid $B$ also forms a white crystalline solid with sodium hydrogensulphite but it does not give a test with ammoniacal silver nitrate. Which of the two liquids is an aldehyde? Write the chemical equations of these reactions also.

Reactant of Column-$I$ when reacted with acetaldehyde in the presence of $H^{+}$ gives the product given in Column-$II$ and their names are given in Column-$III$. Match the reactants in Column-$I$ with the products in Column-$II$ and their names in Column-$III$.

Column-$I$ (Reagent)	Column-$II$ (Product) and Column-$III$ (Name)
$A$. Ammonia $(NH_{3})$	$i$. $CH_{3}CH=NCH_{3}$; $m$. Acetaldehyde hydrazone
$B$. Amine $(CH_{3}NH_{2})$	$ii$. $CH_{3}CH=NNH_{2}$; $n$. Acetaldehyde oxime
$C$. Hydroxyl amine $(NH_{2}OH)$	$iii$. $CH_{3}CH=NH$; $o$. Acetaldehyde imine
$D$. Hydrazine $(NH_{2}NH_{2})$	$iv$. $CH_{3}CH=NOH$; $q$. Acetaldehyde methyl imine

The major product formed in the following reaction is:

Splitting of signals in $NMR$ spectroscopy is caused by