Which of the following reactions uses sodium cyanide $(NaCN)$ as a catalyst?

Which of the following reagents must be used in the given interconversion? The reaction involves the reduction of $4$-hydroxycyclohexanone to cyclohexanol,where the carbonyl group is reduced to a methylene group while the hydroxyl group remains unaffected.

Aromatic aldehydes are converted into acyloins in the presence of cyanide ions as a catalyst. What is this reaction called?

Primary aldehyde on oxidation gives

The reagent used for the separation of acetaldehyde from acetophenone is

Acetaldehyde reacts with $Cl_2$ (in excess) to give