What accelerating potential must be imparted to a proton beam to …

$(I)$ $\begin{array}{*{20}{c}}
{O\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{||\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{O - S - {C_6}{H_4} - C{H_3}} \\
{||\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{O\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}\,$ $(II)$ $\begin{array}{*{20}{c}} {O\,\,\,\,\,\,\,} \\ {||\,\,\,\,\,\,\,} \\ {O - S - {C_6}{H_5}} \\ {||\,\,\,\,\,\,\,} \\ {O\,\,\,\,\,\,\,} \end{array}\,$$(III)$ $N_3$ $(IV)$ $Br$

→

$\begin{matrix}
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O \\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|| \\
HO-\underset{(3)}{\mathop{C{{H}_{2}}}}\,-\underset{(2)}{\mathop{C{{H}_{2}}}}\,-\underset{(1)}{\mathop{C}}\,-H \\
\end{matrix}$

Which conformer of above compound is most stable (consider conformer across $(C_2 -C_3)$

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A compound was synthesized by a student, but its structure was not identified. However, his wonderfully helpful instructor told him that it was a meso compound with $5$ carbons and $2$ stereogenic centers. Which of the following structures should the student consider as possibilities for his compound ?