The isomer$(s)$ of $[Co(NH_{3})_{4}Cl_{2}]^{+}$ that has/have a $Cl-Co-Cl$ angle of $90^{\circ}$ is/are:

Which of the following complexes does not show optical isomerism?

Identify the incorrect match from the following:

Number of complexes from the following with an even number of unpaired $d$ electrons is . . . . . . . . . .
$[V(H_2O)_6]^{3+}, \quad [Cr(H_2O)_6]^{2+}, \quad [Fe(H_2O)_6]^{3+}, \quad [Ni(H_2O)_6]^{3+}, \quad [Cu(H_2O)_6]^{2+}$
[Given atomic numbers: $V=23, Cr=24, Fe=26, Ni=28, Cu=29$]

Which of the following complexes shows ionization isomerism?

The magnetic moment of the complexes is zero in: