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

The molecules represented by the above two structures are

Which of the following cyclopentane derivative is optically inactive ?

How many different stereoisomers are possible for the following compound ?

$\begin{array}{*{20}{c}}
H\\
|\\
{ClHC = HC - C - CH = CHCl}\\
|\\
{Cl}
\end{array}$

How are the following compounds related ?

Which of the following molecule contains asymmetric carbon atom