Which of the following has the lowest enol content?

The product formed in the following reaction is:
$CHO-CH(OH)-CH_2OH \xrightarrow{2HIO_4} ?$

Benzene on reaction with $A$ forms acetophenone,which on reaction with $B$ forms ethylbenzene. $A$ and $B$ are:

An aldehyde or ketone containing at least one $\alpha-H$ atom reacts with dilute $NaOH$ to form a $\beta-$hydroxy aldehyde or $\beta-$hydroxy ketone. This reaction is known as $—$

$A$ and $B$ are isomers; Isomer $B$ is

Which of the following cannot be obtained by the reduction of an aldehyde or a ketone using $NaBH_4$ or $LiAlH_4$?