What is stereoisomerism ? Which are its types ? 

The compounds that have the same constitution and sequence of covalent bonds but differ in relative positions of their atoms or groups in space are called stereoisomers. This special type of isomerism is called as stereoisomerism and can be classified as geometrical and optical isomerism. Stereoisomerism can be classified in two types.

$(i)$ geometrical

$(ii)$ optical isomerism