Which of the following structures is not meso-$2,3$-butanediol?

$A$ compound was synthesized by a student,but its structure was not identified. However,his 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?

Which of the following are meso compounds?

Consider the sets $I$,$II$,and $III$. Identify the set$(s)$ which is (are) correctly matched.
$I$. $\text{Staggered ethane} > \text{eclipsed ethane} \dots \dots \dots \text{torsional strain}$.
$II$. $2, 2-\text{Dimethylbutane} > 2-\text{methylpentane} \dots \dots \dots \text{boiling point}$.
$III$. $cis-\text{but}-2-\text{ene} > trans-\text{but}-2-\text{ene} \dots \dots \dots \text{dipole moment}$.

From the given compounds $(A)$,$(B)$,$(C)$,and $(D)$,which one is chiral?

The relationships between the pairs of compounds shown below are respectively: