Benzoin is

$CaOCl_2 + H_2O \longrightarrow Ca(OH)_2 + X$
$X + CH_3CHO \longrightarrow Y$
$Y + Ca(OH)_2 \longrightarrow CHCl_3$
What is '$Y$'?

Compound '$A$' (molecular formula $C_3H_8O$) is treated with acidified potassium dichromate to form a product '$B$' (molecular formula $C_3H_6O$). '$B$' forms a shining silver mirror on warming with ammoniacal silver nitrate. '$B$' when treated with an aqueous solution of $H_2NCONHNH_2 \cdot HCl$ and sodium acetate gives a product '$C$'. Identify the structure of '$C$.

The structure of $A$ in the given reaction is:

$C_6H_5-CH=CHCHO \xrightarrow{X} C_6H_5-CH=CHCH_2OH$. In the above sequence,$X$ can be:

The reactivity towards nucleophilic addition reaction of
$(I) HCHO$,
$(II) CH_3CHO$,
$(III) CH_3COCH_3$ is