Why are cis and trans isomers of succinic acid impossible?

            Due to the absence of double bond in Succinic Acid.

Explanation:

                  cis-trans Isomerism also known as Geometrical Isomerism is a type of isomerism in which isomers have same molecular formula and structural formula but differ in respect of arrangement of groups or atoms about the double bond.

                 Therefore, a double bond is the main requirement for such isomerism process.

Example:

              cis and trans Butene. In cis-Butene both methyl groups are located on the same side. While, in trans-Butene both methyl groups are in opposite directions (Figure red).

Result:

          As shown in figure, succinic acid (blue) is lacking a double bond. Therefore, it fails to show cis-trans isomerism.

if two electrons have the same n, the same ℓ, and the same ml, then they are in the same orbital. the pauli exclusion principle states that no two identical fermions (a fancy word for electrons and other subatomic particles like electrons) may occupy the same quantum state in an atom simultaneously.