Which reagent turns pink in the presence of an aldehyde?

When acetaldehyde is heated with Fehling solution,a red precipitate is formed. Which of the following is that?

Two aliphatic aldehydes $P$ and $Q$ react in the presence of aqueous $K_2CO_3$ to give compound $R$,which upon treatment with $HCN$ provides compound $S$. On acidification and heating,$S$ gives the product shown below:
$1.$ The compounds $P$ and $Q$ respectively are:
$2.$ The compound $R$ is:
$3.$ The compound $S$ is:
Give the answer for questions $1$,$2$ and $3$.

What is the product of the Clemmensen reduction of $3-nitroacetophenone$?

Amongst the following compounds,the one that will not respond to Cannizzaro reaction upon treatment with alkali is

What is the reduction of aldehydes and ketones in the presence of zinc amalgam and concentrated $HCl$ called?