Question

What are two types of stereoisomerism?

Answer 1

Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer.
The two main types of stereoisomerism are: DiaStereomerism (including 'cis-trans isomerism') Optical Isomerism (also known as 'enantiomerism' and 'chirality').

Cis-trans isomerism- Cis/trans isomerism occurs when a double bond is present, because the pi bond involved prevents that bond from being "twisted" the same way that a single bond can be.
A good example is 1,2-dichloroethene: $C_2{H}_{2}C{l}_2$.

Optical Isomerism- Optical isomers are stereoisomers formed when asymmetric centers are present, for example, a carbon with four different groups bonded to it.
Enantiomers are two optical isomers (i.e. isomers that are reflections of each other).