Question

Pick out the correct statements from the following
1. Cobalt $(III)$ is more stable in octahedral complexes
2. Zinc forms coloured ions or complexes
3. Most of the d-block elements and their compounds are ferromagnetic
4. Osmium shows $(VIII)$ oxidation state
5. Cobalt $(II)$ is more stable in octahedral complexes

• A. $1$ and $2$
• B. $1$ and $3$
• C. $2$ and $4$
• D. $1$ and $4$
• E. $2$ and $5$

Answer 1

Answer: (D)

1. $C{o}^{3+}$ have higher charge density than $C{o}^{2+}$ so $C{o}^{3+}$ is more stable in octahedral complexes.
2. Zn exhibits only +2 oxidation state. So
$Z{n}^{2+}=[Ar]3d^{10},4s^0$
Since it does not contain any unpaired electron, its compounds are colorless.
3. d-block elements are generally paramagnetic and sometimes, but not ferromagnetic
4. Osmium and ruthenium are VIII group elements, so can exhibit the highest oxidation state +8 in their oxides, eg, $Os{O}_4$ .
Hence, statement 1 and 4 are correct.