Which one of the following has an optical isomer? (en = ethylenediamine)

1. $[\text{Co}(\text{en}{)}_3{]}^{3+}$: This is an octahedral complex of the type $[M(aa{)}_3]$. It lacks any plane of symmetry and exists as a pair of non-superimposable mirror images (d and l forms). It is optically active.2. $[\text{Zn}(\text{en})({\text{NH}}_3{)}_2{]}^{2+}$: Tetrahedral complexes of Zn with unsymmetrical ligands might be chiral, but here with two ${\text{NH}}_3$, there is a plane of symmetry.3. $[\text{Co}({\text{H}}_2\text{O}{)}_4(\text{en}){]}^{3+}$: Has a plane of symmetry.4. $[\text{Zn}(\text{en}{)}_2{]}^{2+}$: Tetrahedral, has a plane of symmetry.