Which of the following compounds is used to convert acetaldehyde into acetaldehyde cyanohydrin?

Identify $(A)$ in the following reaction sequence:
$\mathop {(A)}\limits_{\text{gives positive iodoform Test}}$ $\xrightarrow[(ii) H^{+}, H_2O, (iii) \text{conc. } H_2SO_4/\Delta ]{(i) CH_3MgBr} (B)$ $\xrightarrow{O_3/Zn, H_2O}$

$CH_3-CO-CH_2-COOCH_3$ $\xrightarrow[H_2O]{H^{+}} A$ $\xrightarrow{\Delta} B$ $\xrightarrow{HCN} C$. What are $B$ and $C$?

An organic compound $CH_3-CH=CH-CH_2-CHO$ is taken in two different containers $A$ and $B$. Sample in $A$ is treated with $H_2 / Ni$ forming new compound $P$. Sample in $B$ is treated with $LiAlH_4$ and hydrolyzed further forming new compound $Q$. Identify $P$ and $Q$.

$4$-formylbenzoic acid on treatment with one equivalent of hydrazine followed by heating with alc. $KOH$ gives the major product:

Given below are the four isomeric compounds $(P, Q, R, S)$. Identify the correct statements from below.
$A$. $Q, R$ and $S$ will give a precipitate with $2,4-DNP$.
$B$. $P$ and $Q$ will give a positive Bayer's test.
$C$. $Q$ and $R$ will give a sooty flame.
$D$. $R$ and $S$ will give a yellow precipitate with $I_2/NaOH$.
$E$. $Q$ alone will deposit silver with Tollen's reagent.
Choose the correct option.