Which of the following structures show constitutional isomers of $1,2-$dichloropentane?

 I   

 II   

 III   

 IV    

V  

How many stereoisomers of $1, 2-$dichlorocyclohexane are optically active?

${\mathrm{C}}_3{\mathrm{H}}_6{\mathrm{Br}}_2$ can show:

$\mathrm{A}$ and $\mathrm{B}$ are a pair of what?

The lowest molecular weight alkene which is optically active is/are

(a) $3$-methyl pentene

(b) $2$-methyl pent-$2$-ene

(c) $4$-methyl pentene

(d) $3$-methyl butene

(e) $3$-methyl hex-$2$-ene