The structures of maleic and fumaric acids are given below
The structures of fumaric and maleic acid suggest that they are geometrical isomers because they have same molecular formula but different spatial arrangement of atoms around a double bond
When the similar groups are present on same side of double bond, the isomer is called cis and when different groups are present on same side of double bond, then the isomer is called trans. Hence, maleic acid is cis form and fumaric acid is trans form.
