Benzaldehyde condenses with $N,N$-dimethylaniline in the presence of anhydrous $ZnCl_2$ to give:

Ketones react with $Mg-Hg$ followed by treatment with water to give:

Give the major organic product of the following reaction.

Which one of the following compounds will give an orange precipitate when treated with $2,4-$dinitrophenylhydrazine?

$A$ carbonyl compound $P$,which gives a positive iodoform test,undergoes reaction with $MeMgBr$ followed by dehydration to give an olefin $Q$. Ozonolysis of $Q$ leads to a dicarbonyl compound $R$,which undergoes intramolecular aldol reaction to give predominantly $S$.
$P$ $\xrightarrow[\substack{2. H^{+}, H_2 O \\ 3. H_2 SO_4, \Delta}]{1. MeMgBr} Q$ $\xrightarrow[2. Zn, H_2 O]{1. O_3} R$ $\xrightarrow[2. \Delta]{1. OH^{-}} S$
$1.$ The structure of the carbonyl compound $P$ is
$2.$ The structures of the products $Q$ and $R$,respectively,are
$3.$ The structure of the product $S$ is
Give the answer for questions $1, 2$ and $3.$

$A$ compound $A$ has the molecular formula $C_2Cl_3OH$. It reduces Fehling's solution and on oxidation,it gives a monocarboxylic acid $B$. Compound $A$ is also obtained by the reaction of ethanol with chlorine. What is $A$?