To determine which metal carbonyls are inner orbital complexes with diamagnetic properties, let's analyze the electron configurations of the metal atoms in each compound:
(i) Ni(CO)4: Nickel (Ni) has 28 electrons (1s^2 2s^2 2p^6 3s^2 3p^6 3d^8 4s^2), and each CO ligand donates 2 electrons (a total of 8 electrons). The resulting complex has 36 electrons. Ni(0) has 28 electrons, but Ni(CO)4 has 8 more, leading to an oxidation state of +8. Since 36 is even, the complex is diamagnetic, and it's an inner orbital complex.
(ii) Fe(CO)5: Iron (Fe) has 26 electrons (1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2), and each CO ligand donates 2 electrons (a total of 10 electrons). The resulting complex has 36 electrons. Fe(0) has 26 electrons, but Fe(CO)5 has 10 more, leading to an oxidation state of +10. Since 36 is even, the complex is diamagnetic, and it's an inner orbital complex.
(iii) V(CO)6: Vanadium (V) has 23 electrons (1s^2 2s^2 2p^6 3s^2 3p^6 3d^3 4s^2), and each CO ligand donates 2 electrons (a total of 12 electrons). The resulting complex has 35 electrons. V(0) has 23 electrons, but V(CO)6 has 12 more, leading to an oxidation state of +12. Since 35 is odd, the complex is paramagnetic, and it's not an inner orbital complex.
(iv) Cr(CO)6: Chromium (Cr) has 24 electrons (1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^1), and each CO ligand donates 2 electrons (a total of 12 electrons). The resulting complex has 36 electrons. Cr(0) has 24 electrons, but Cr(CO)6 has 12 more, leading to an oxidation state of +12. Since 36 is even, the complex is diamagnetic, and it's an inner orbital complex.
So, the correct answer is (D) I and II only.
