A complex whose IUPAC name is not correctly written is :

The IUPAC name of the complex Fe(σ−C_5​H₅​)₂​ is Bis(η¹-cyclopentadienyl)iron(0) and not Bis(η⁵-cyclopentadienyl)iron(0).
this is because the ligand is attached to metal through sigma bond only. Thus option 1 is incorrectly named.
The IUPAC name of the complex Cr(C_6​H₆​)₂​ is Bis(η⁵-benzene)chromium(0). In this complex, the ligand is attached to metal ion through pi bonds.
Thus option 2 is correctly named.
The IUPAC name of the compound [CoCl​₂(H_2​O)₄​]Cl.2H₂​O is tetraaquadichlorocobalt(III)chloride-2-water.
The prefix tetra indicates four ligands and the prefix di indicates two ligands. The ligands are named in alphabetical order.
Thus option 3 is correctly named.
The IUPAC name of the complex [Zn(NCS)_4​]²⁻ is tetrathiocyanato-N-zincate(II)ion.
Here N represents the linkage through N atom of thiocyanato group.The prefix tetra indicates four ligands. For complex anion, the name of the zinc is written as zincate.
Thus option 4 is correctly named