What is reactant $A$?

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

What is the product obtained in the reaction?
$CH_3-CH=CH-CH_2-CHO \xrightarrow[(ii) H_3O^{+}]{(i) LiAlH_4} \text{product}$

Which of the following compounds will give a yellow precipitate with iodine and alkali?

The major product $(P)$ in the following reaction is $:$

$3$-hydroxybutanal is formed when $(X)$ reacts with $(Y)$ in a dilute $(Z)$ solution. What are $X, Y$ and $Z$?