Which one of the following reactions can be used for the preparation of $\beta$-hydroxy acid derivatives?

Which one of the following reactions does not represent the correct combination of substrate and product under the given conditions?

$A$ compound contains an $\alpha$-hydrogen atom and forms a $\beta$-hydroxy aldehyde in the presence of a dilute alkali. When this product is heated with a dilute acid,it yields unsaturated crotonaldehyde. Identify the compound.

The product of the following reaction is :

Identify the products of the following reaction:
$HCHO + C_6H_5CHO \xrightarrow[ii. \ H_3O^+]{i. \ conc. \ NaOH} ?$

Reaction of formaldehyde and ammonia gives