What is the reaction of benzaldehyde with aniline called?

The most appropriate reagent to distinguish between acetaldehyde and formaldehyde is

The structure of $A$ in the given reaction is:

The end product $(C)$ in the following sequence of reactions is:
$HC \equiv CH$ $\xrightarrow[20\% \ H_2SO_4]{1\% \ HgSO_4} A$ $\xrightarrow[H_2O]{CH_3MgX} B$ $\xrightarrow{[O]} (C)$

The reaction $R-C(=O)-R + HCN \xrightarrow{\text{catalyst}} R-C(OH)(CN)-R$ is a nucleophilic addition reaction. Which of the following can be used as a catalyst in the above reaction?

Which pair never represents $X$ and $Y$ in the following reaction?
Reaction: $X \xrightarrow{Y} CHCl_3 + Z$