Total number of geometrical isomers of $[Ma_3b_3]$ is/are:

The total possible coordination isomers for the following compounds respectively are :
$[Co(en)_3] [Cr(C_2O_4)_3]$
$[Cu(NH_3)_4] [CuCl_4]$
$[Ni(en)_3] [Co(NO_2)_6]$

Which among the following complexes has the maximum number of isomers?

Which of the following statements is not correct?

The electronic configurations of $Cr^{2+}$,$Mn^{2+}$,$Fe^{2+}$,and $Co^{2+}$ ions are $d^4$,$d^5$,$d^6$,and $d^7$ respectively. Which of the following complexes has the minimum paramagnetic character?

Which of the following octahedral complexes does not exhibit geometrical isomerism? ($A$ and $B$ are monodentate ligands)