Answer
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Work Step by Step
Structural isomers have the same molecular formula but different in structure.
Geometric isomers are formed when two same groups are either on the same side (cis)or opposite side (trans) of a double bond.
Optical isomers are formed when at least one chiral C atom is present in the molecule. Chiral Carbon means that Carbon atom is bonded with four different groups.
a) This is the formula of alkene/ cycloalkane. General formula of Alkenes/Cycloalkanes are : $C_{n}H_{2n}$.
Alkene exhibits structural isomerism as well as geometric (cis-trans) isomerism but not optical isomerism due to absence of chiral C atoms.
Example:
1-hexene, 2-hexene, 3-hexene etc. are structural isomers of $C_{6}H_{12}$.
Among them, 3-hexene is an example which exhibits cis trans isomerism.
b) $C_{5}H_{12}O$ is either ether or alcohol (General formula same : $C_{n}H_{2n+2}O$)
So, it exhibits structural isomerism. example: ethyl propyl ether and pentanol have the same formula but different structure due to different functional group present i.e. they are isomer to each other.
Alcohol or ether does not participate in geometric isomerism due to absence of double bond.
optical isomerism shown by those compounds that have one Chiral C atoms. example: 2-pentanol shows optical isomerism.
c) $C_{6}H_{4}Br_{2}$ : Phenyl group present here.
It exhibits structural isomerism. Example: o-dibromobenzene, m-dibromobenzene and p-dibromobenzene show structural isomerism.
Geometric and optical isomerism are not present here.
