Which of the following does not give a silver mirror test with ammoniacal $AgNO_3$ solution?

What is the correct order of acidic strength?

$A$ 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.

$HCOOH$ reacts with conc. $H_2SO_4$ to produce:

In the reaction,$C_6H_5CHO + (CH_3CO)_2O \xrightarrow{CH_3COONa} (A)$,product $(A)$ is

Which one is the strongest acid?