The correct order of acidic strength among the following is:

$A$ compound $(A)$ has the molecular formula $C_2H_4O_2$ and it gives the following reactions:
$(i)$ Addition of the above compound to a sodium carbonate solution gives effervescence of $CO_2$ gas and forms compound $(P)$.
$(ii)$ When compound $(P)$ is heated with sodalime,it gives gas $(Q)$. Identify $(A)$,$(P)$,and $(Q)$ and provide the reactions.

When propionic acid is reacted with aqueous sodium carbonate,$CO_2$ is released. From where does the $'C'$ of $CO_2$ come?

Identify the most acidic hydrogen in the given compound.

Bouveault-Blanc reduction reaction involves:

In which of the following reactions will cyanide be obtained as a major product?