What is the geometry of $[Ni(CO)_4]$?

For the coordination compound $[Co(NH_3)_5CO_3]ClO_4$,what are the coordination number,oxidation state,number of electrons in the $d$-orbitals,and the number of unpaired electrons for the central metal $Co$?

In which of the following complex ions is the central metal atom's $d$-orbital devoid of electrons?

Which of the following complexes has $dsp^2$ hybridisation?

Hybridization in $[Ni(CO)_4]$ and $[Ni(CN)_4]^{2-}$ are respectively . . . . . . .

Using valence bond theory,explain the following in relation to the complexes given below: $[Mn(CN)_{6}]^{3-}, [Co(NH_{3})_{6}]^{3+}, [Cr(H_{2}O)_{6}]^{3+}, [FeCl_{6}]^{4-}$
$(i)$ Type of hybridisation.
$(ii)$ Inner or outer orbital complex.
$(iii)$ Magnetic behaviour.
$(iv)$ Spin only magnetic moment value.