Question

The number of isomers of ${{\rm{C}}_{\rm{5}}}{{\rm{H}}_{{\rm{10}}}}$ is?
A.10
B.11
C.12
D.13

Answer 1

Hint:
Isomers are compounds having the same structural formula but different arrangement of atoms in a molecule.Isomers are classified into two types -structural isomers and stereoisomers.

Complete step by step answer:
-We know that the name of the compound ${{\rm{C}}_{\rm{5}}}{{\rm{H}}_{{\rm{10}}}}$ is pentene. This compound has a total of 13 isomers. Out of these 13 isomers, 10 are structural and geometrical isomers and three of them are optical isomers.
-The structural isomers include, pent-1-ene, (E)-pent-2-ene, (Z)-pent-2-ene, 2-methylbut-1-ene, 2-methylbut-2-ene, 2-methylbut-1-ene, cyclopentane, methylcyclobutane, 1,1-dimethylcyclopropane, ethyl cyclopropane, 1,2-dimethylcyclopropane. The three optical isomers include (1R,2S)-1,2-dimethylcyclopropane, (1S,2S)-1,2- dimethyl cyclopropane, (1R,2R)-1,2-dimethylcyclopropane.
We can draw the structure of these 13 isomers in the following way.

      pent-1-ene (E)-pent-2-ene (Z)-pent-2-ene 2-methylbut-1-ene

2-methylbut-2-ene 2-methylbut-1-ene cyclopentane methylcyclobutane
         

1,1-dimethylcyclopropane ethyl cyclopropane 1,2-dimethylcyclopropane
-The ten structures given above are the structural isomers of the compound ${{\rm{C}}_{\rm{5}}}{{\rm{H}}_{{\rm{10}}}}$

(1R,2S)-1,2-dimethylcyclopropane (1S,2S)-1,2- dimethyl cyclopropane

(1R,2R)-1,2-dimethylcyclopropane.
The three structures given above are the optical isomers of the compound ${{\rm{C}}_{\rm{5}}}{{\rm{H}}_{{\rm{10}}}}$.
Now, lets see that there are 13 isomers that can be drawn for the compound${{\rm{C}}_{\rm{5}}}{{\rm{H}}_{{\rm{10}}}}$,therefore, out of the given four options, D is the correct option. A, B and C are incorrect options.

Note:
Students may get confused while identifying structural and optical isomers. It is important to note that structural isomers are those isomers of a compound that has the same structural formula, but in the isomers, the arrangements of the groups in the compounds are different, while optical isomers are identified by the interaction they have with that of the plane polarized light. The optical isomers are usually non superimposable mirror images of each other.