$2CD_2=O + OH^- \xrightarrow{\quad} X + Y$ ($Y$ is an alcohol and $D$ is deuterium). Identify $X$ and $Y$.

Which of the following carbonyl compounds does $NOT$ undergo aldol condensation?

Which of the following compounds on reaction with ammoniacal silver nitrate solution forms a precipitate of silver?

Formalin is the commercial name of

$A$ 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 that shows positive iodoform test is