Which of the following is optically active?

Solutions of optically active isomers rotate the plane of polarized light in a polarimeter. Match the following columns $(I)$ with $(II), (III)$,and $(IV)$ correctly:

$(I)$ Optical Activity	$(II)$ Form	$(III)$ Sign	$(IV)$ Rotation
$(A)$ Dextrorotatory	$d$	$(+)$	Right
$(B)$ Laevorotatory	$l$	$(-)$	Left
$(C)$ Optically Inactive (Racemic)	$dl$	$(\pm)$	Zero rotation

Which of the following compounds is optically inactive?

How many meso isomers of $C_4H_8Cl_2$ are possible?

The necessary and sufficient condition for the existence of enantiomers is ...........

How many optically active stereoisomers are possible for butan-$2,3$-diol?