What are $X$ and $Y$ in the following reactions?

$3$ moles of ethanol react with $1$ mole of phosphorus tribromide to form $3$ moles of bromoethane and $1$ mole of $X$. Which of the following is $X$?

$CHO-CH(OH)-CH_2OH \xrightarrow{2HIO_4}$ Products obtained in the above reaction are

Denatured alcohol is:

In the following reaction sequence,the compound $I$ is:
$I (C_3H_6Cl_2)$ $\xrightarrow{KOH_{(aq)}} II$ $\xrightarrow{(i) CH_3MgBr, (ii) H_2O/H^{+}} III$ $\xrightarrow{Anhy. ZnCl_2 + Conc. HCl}$ gives turbidity immediately.

$A$ compound with the formula $C_4H_{10}O$ reacts with sodium and upon oxidation gives a carbonyl compound that does not reduce Tollen's reagent. What is the original substance?