Which of the following complex ions does not contain any $d$-electrons in the central metal atom?

The paramagnetic complex ion which has no unpaired electrons in $t_{2g}$ orbitals is

The coordination environment of $Ca^{2+}$ ion in its complex with $EDTA^{4-}$ is:

How many unpaired electrons are present in the central metal ion of $[CoCl_4]^{2-}$?

Give the correct sequence of initials $T$ or $F$ for the following statements. Use $T$ if the statement is true and $F$ if it is false.
$(I) \ Co(III)$ is stabilized in the presence of weak field ligands,while $Co(II)$ is stabilized in the presence of strong field ligands.
$(II)$ Four-coordinated complexes of $Pd(II)$ and $Pt(II)$ are diamagnetic and square planar.
$(III) \ [Ni(CN)_4]^{4-}$ ion and $[Ni(CO)_4]$ are diamagnetic tetrahedral and square planar respectively.
$(IV) \ Ni^{2+}$ ion does not form inner orbital octahedral complexes.

The hybridisations of $Ni(CO)_4$ and $[Cr(H_2O)_6]^{2+}$ respectively,are