Number of identical $Cr-O$ bonds in dichromate ion $Cr_2O_7^{2-}$ is

Which of the following systems in an octahedral complex has the maximum number of unpaired electrons?

Which of the following statements is not correct?

The geometries of $Ni(CO)_4$ and $Ni(PPh_3)_2Cl_2$ are:

For octahedral $Mn(II)$ and tetrahedral $Ni(II)$ complexes,consider the following statements:
$(I)$ Both the complexes can be high spin.
$(II)$ $Ni(II)$ complex can very rarely be low spin.
$(III)$ With strong field ligands,$Mn(II)$ complexes can be low spin.
$(IV)$ Aqueous solution of $Mn(II)$ ions is yellow in color.

Which of the following facts about the complex $[Cr(NH_3)_6]Cl_3$ is wrong?