Q. Pick out the correct statements from the following. Cobalt (III) is more stable in octahedral complexes. Zinc forms coloured ions or complexes. Most of the $d$-block elements and their compounds are ferromagnetic. Osmium shows (VIII) oxidation state. Cobalt (II) is more stable in octahedral complexes.
A) 1 and 2
B) 1 and 3
C) 2 and 4
D) 1 and 4
Explanation
(d)
${CO}^{3 +}$ have higher charge density than ${CO}^{2 +}$, so ${CO}^{3 +}$ is more stable in octahedral complexes.
(ii) Zn exhibits only +2 oxidation state. So,
${Zn}^{2 +}$=[Ar]3$d^{10}$, 4$s^{0}$
Since, it does not contain any unpaired electron, its compounds are colourless.
(iii) $d$-block elements are generally paramagnetic and sometimes diamagnetic, but not ferromagnetic.
(iv) Osmium and ruthenium are VIII group elements, so can exhibit the highest oxidation state +8 in their oxides, e.g., ${OsO}_{4}$.
Hence, statement 1 and 4 are correct.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.