Which of the following compounds shows tautomerism?

$OCH-CHO \xrightarrow{OH^{-}} HOCH_2-COO^-$. The reaction given is:

In the reaction sequence,
the major products $X$ and $Y$ respectively are

Formaldehyde can be distinguished from acetaldehyde by the use of

Arrange the following compounds in the increasing order of their equilibrium constants for the formation of a hydrate:
$(I)$ $6$-amino-$1$-tetralone
$(II)$ $7$-amino-$1$-tetralone
$(III)$ $1$-tetralone
$(IV)$ $6$-nitro-$1$-tetralone

In $3-Methyl-2-cyclohexenone$,which hydrogen cannot undergo deuterium exchange when it reacts with $CH_3O^{-} / CH_3OD$?