Acetaldehyde, when heated in the presence of sodium hydroxide and $I_2$, forms:

In the given compounds,which one does not give the silver mirror test?

The reaction of hydrazine $(NH_2NH_2)$ with aldehydes and ketones yields a compound with the general structure:

Hex$-4-$en$-2-$ol on treatment with $PCC$ gives $'A'.$ $'A'$ on reaction with sodium hypoiodite gives $'B',$ which on further heating with soda lime gives $'C'.$ The compound $'C'$ is $....... .$

An alkene $A$ $(C_4H_8)$ exhibits cis/trans isomerism. $A$ on ozonolysis gives $B$,which when reacted with $NaOH$ followed by hydroxylamine gives $C$. What are $B$ and $C$?

How will you convert ethanal into the following compounds?
$(i)$ Butane$-1,3-$diol
$(ii)$ But$-2-$enal
$(iii)$ But$-2-$enoic acid