Which of the following complexes will show the largest splitting of $d$-orbitals?

What will be the correct order for the wavelengths of absorption in the visible region for the following complexes: $[Ni(NO_{2})_{6}]^{4-}, [Ni(NH_{3})_{6}]^{2+}, [Ni(H_{2}O)_{6}]^{2+}$?

In which case is a $d^7$ complex species more stable?

The $d-$orbital electronic configuration of the complex among $[Co(en)_3]^{3+}$,$[CoF_6]^{3-}$,$[Mn(H_2O)_6]^{2+}$ and $[Zn(H_2O)_6]^{2+}$ that has the highest $CFSE$ is $:$

An ion $M^{2+}$ forms the complexes $[M(H_2O)_6]^{2+}$,$[M(en)_3]^{2+}$,and $[MBr_6]^{4-}$. Match the complex with the appropriate colour.

In an octahedral crystal field,the $t_{2g}$ orbitals are: