What is the geometry of the $[Fe(CO)_5]$ complex?

Which of the following compounds has a tetrahedral geometry?

Which of the following complexes does not exhibit $d^2sp^3$ hybridization?

An octahedral complex is formed when hybrid orbitals of the following type are involved:

Which of the following complexes exhibits a square planar geometry?

An aqueous solution of $NiCl_{2}$ was heated with excess sodium cyanide in the presence of a strong oxidizing agent to form $[Ni(CN)_{6}]^{2-}$. The total change in the number of unpaired electrons on the metal centre is $.....$