Identify the correct orders among the following:

The correct statements with respect to the above pair of reactions are that:
$(I)$ The reactions are stereospecific.
$(II)$ $(X)$ is erythro and $(Y)$ is threo isomer.
$(III)$ $(X)$ is threo and $(Y)$ is erythro isomer.
$(IV)$ Each of $(P)$ and $(Q)$ gives a mixture of $(X)$ and $(Y)$.

Which of the following is not correctly matched?

The hydrogen indicated by the arrow will be easily removed as:

Examine the following three pairs of possible isomers. Now state whether the pairs represent identical compounds or different isomers.

The possible number of stereoisomers of the product of the following reaction would be: $Ph - CH = CH - CH(CH_3) - CHO \xrightarrow[pH = 4.5]{H_2N - OH}$ ?