Identify the final product in the following reaction sequence: $R-CHO$ $\xrightarrow{HS-(CH_2)_3-SH}$ $\xrightarrow{n-BuLi}$ $\xrightarrow{D_2O}$ $\xrightarrow{HgCl_2/CdCO_3, H_2O} \text{Product}$

Which of the following aldehydes is most reactive $?$

Which one of the following reacts with $HCN$ and Tollen's reagent,but is not oxidised by Fehling's solution?

$A$ compound $A$ with molecular formula $C_{10}H_{13}Cl$ gives a white precipitate on adding silver nitrate solution. $A$ on reacting with alcoholic $KOH$ gives compound $B$ as the main product. $B$ on ozonolysis gives $C$ and $D$. $C$ gives Cannizzaro reaction but not aldol condensation. $D$ gives aldol condensation but not Cannizzaro reaction. $A$ is:

$CH_3-CHO$ $\xrightarrow{HCN} (A)$ $\xrightarrow{H_3O^{+}} (B)$ $\xrightarrow{\Delta} (C)$ $\xrightarrow{LiAlH_4} (D)$ $\xrightarrow{HIO_4} HCHO + (E)$. Compound $(C)$ can show geometrical isomerism. Product $(E)$ of the reaction will be:

$A$ compound has a vapour density of $29$. On warming with an aqueous solution of alkali,it gives a yellow precipitate. The compound is