If the number of structural isomers of molecular formula ${\mathrm{C}}_2{\mathrm{H}}_2{\mathrm{Br}}_2$ is$\text{'}\mathrm{x}\text{'}$ and the number of stereo isomers is $\text{'}\mathrm{y}\text{'},$ then what will be the value of $\mathrm{xy}$?

What does the following Newman projection represent?

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

 I   

 II   

 III   

 IV    

V