The correct statements about metal carbonyls are

A. The metal-carbon bonds in metal carbonyls possess both $\sigma$ and $\pi$ character.

B. Due to synergic bonding interactions between metal and CO ligand, the metal-carbon bond becomes weak.

C. The metal-carbon $\sigma$ bond is formed by the donation of lone pair of electrons on the carbonyl carbon into a vacant orbital of metal.

D. The metal-carbon $\pi$ bond is formed by the donation of electrons from filled d-orbital of metal into vacant $\pi^*$ orbital of CO .

Choose the correct answer from the options given below :

Given below are two statements:

Statement I: Each electron in $\mathrm{e}_{\mathrm{g}}$ orbitals destabilizes the orbitals by $+0.6 \Delta_{\mathrm{o}}$ and each electron in the $t_{2 g}$ orbitals stabilizes the orbitals by $-0.4 \Delta_0$ in an octahedral field on the basis of crystal field theory.

Statement II: All the d - orbitals of the transition metals have the same energy in their free atomic state but when a complex is formed the ligands destroy the degeneracy of these orbitals on the basis of crystal field theory.

In the light of the above statements, choose the correct answer from the options given below

Consider the metal complexes $\left[\mathrm{Ni}(\mathrm{en})_3\right]^{2+}(\mathrm{A}),\left[\mathrm{NiCl}_4\right]^{2-}(\mathrm{B})$ and $\left[\mathrm{Ni}\left(\mathrm{NH}_3\right)_6\right]^{2+}(\mathrm{C})$. Choose the CORRECT option by considering the number of unpaired electrons present in (A), (B) and (C) respectively and the order of frequency of absorption.

$$ \text { Match the LIST-I with LIST-II } $$

Choose the correct answer from the options given below :