Introduction:
Optical isomerism is a type of stereoisomerism where two molecules are non-superimposable mirror images of each other. This occurs when a molecule has a chiral center, which is a carbon atom bonded to four different groups. In the given options, we need to identify the alkene that has a chiral center and therefore exhibits optical isomerism.

Explanation:
To determine whether an alkene has a chiral center, we need to examine the carbon atoms bonded to the double bond and check if they are all different. Let's analyze each option:

Option a) 3 - methyl - 2 - pentene:
The carbon atoms bonded to the double bond are a methyl group, a hydrogen atom, a methyl group, and a pentyl group. Since there is a methyl group repeated twice, this alkene does not have a chiral center and does not exhibit optical isomerism.

Option b) 4 - methyl - 1 - pentene:
The carbon atoms bonded to the double bond are a hydrogen atom, a methyl group, a pentyl group, and a methyl group. Similarly to option a, this alkene has a methyl group repeated twice and does not have a chiral center.

Option c) 3 - methyl - 1 - pentene:
The carbon atoms bonded to the double bond are a hydrogen atom, a methyl group, a pentyl group, and a hydrogen atom. This alkene has four different groups bonded to the carbon atoms, making it a chiral center. Therefore, option c exhibits optical isomerism.

Option d) 2 - methyl - 2 - pentene:
The carbon atoms bonded to the double bond are a methyl group, a hydrogen atom, a pentyl group, and a methyl group. Similar to options a and b, this alkene has a methyl group repeated twice and does not have a chiral center.

Conclusion:
Out of the given options, only option c, 3 - methyl - 1 - pentene, has a chiral center and exhibits optical isomerism. The other options do not have a chiral center due to the repetition of certain groups bonded to the carbon atoms.

Alkene carbon centre must be chiral and sp3 hybridised and attached with 4different carbons