Phenylmagnesium bromide,upon reaction with a compound $X$ followed by treatment with acid,gives benzyl alcohol. The compound $X$ is

What is the product formed when acetaldehyde reacts with $PCl_5$?

Arrange the following compounds in decreasing order of reactivity towards nucleophilic addition reaction:
$I: HCHO$
$II: CH_3CHO$
$III: CH_3COCH_3$
$IV: PhCOCH_3$

The reaction of $C_6H_5CH=CHCHO$ with $LiAlH_4$ gives

Given below are two statements: Statement $I$: The condensation reaction between $CH_{3} - CH = O$ and $H_{2}N - NH - C(=O) - NH_{2}$ under optimum pH will produce $CH_{3} - CH = N - N(H) - C(=O) - NH_{2}$. Statement $II$: The molecule, $Ph - CH(OH)(OCH_{3})$ will generate $Ph - CH = O$ in the presence of dilute acid. In the light of the above statements, choose the correct answer from the options given below:

Arrange the following compounds in increasing order of their equilibrium constants for hydration:
$(A). CH_3COCH_3, (B). CH_3CHO, (C). ClCH_2COCH_3, (D). HCHO, (E). ClCH_2CHO$