Geometrical and Optical isomerism are types of Stereoisomerism.

Stereoisomerism is a type of isomerism in which compounds have the same molecular formula and connectivity but differ in the arrangement of atoms in space. It arises due to the presence of one or more chiral centers or the presence of restricted rotation around a double bond.

Geometrical isomerism:

Geometrical isomerism occurs when there is restricted rotation around a bond, usually a double bond or a cyclic structure. In such cases, the atoms or groups attached to the double bond or cyclic structure are arranged differently in space, resulting in different isomers.

- Cis-isomer: In a cis-isomer, the similar groups are present on the same side of the double bond or cyclic structure. It is represented by the prefix "cis-". For example, cis-but-2-ene.
- Trans-isomer: In a trans-isomer, the similar groups are present on opposite sides of the double bond or cyclic structure. It is represented by the prefix "trans-". For example, trans-but-2-ene.

Optical isomerism:

Optical isomerism occurs when a molecule has a chiral center, which is an atom bonded to four different groups. Due to this asymmetry, the molecule can exist in two non-superimposable mirror image forms called enantiomers.

- Enantiomers: Enantiomers are mirror image isomers that cannot be superimposed on each other. They have the same physical and chemical properties except for their interaction with plane-polarized light. One enantiomer rotates the plane of polarized light clockwise (dextrorotatory - represented as "+"), while the other enantiomer rotates it counterclockwise (levorotatory - represented as "-").

Key differences between Geometrical and Optical isomerism:

1. Definition: Geometrical isomerism is the arrangement of groups around a double bond or cyclic structure, while optical isomerism is the presence of chiral centers resulting in the existence of enantiomers.

2. Basis: Geometrical isomerism is based on the spatial arrangement of atoms or groups around a bond, while optical isomerism is based on the presence of a chiral center.

3. Rotation: Geometrical isomers do not rotate the plane of polarized light, while optical isomers rotate the plane of polarized light in opposite directions.

4. Superimposability: Geometrical isomers can be superimposed on their mirror image, while optical isomers cannot be superimposed.

In conclusion, geometrical and optical isomerism are both types of stereoisomerism but differ in their basis, properties, and the type of isomer they represent. Geometrical isomers have different spatial arrangements around a bond, while optical isomers have chiral centers resulting in non-superimposable mirror image forms.