Question

Among the following oxides of 3d elements, the number of mixed oxides are ____________.
\[ \mathrm{Ti_2O_3,\ V_2O_4,\ Cr_2O_3,\ Mn_3O_4,\ Fe_3O_4,\ Fe_2O_3,\ Co_3O_4} \]

Hint:

Mixed oxides usually have formulas like \(M_3O_4\) and can be written as a combination of two simpler oxides.

Answer 1

Correct Answer: 3

Step 1: Understand mixed oxides.
A mixed oxide is one that can be represented as a combination of two simple oxides corresponding to different oxidation states of the same metal.

Step 2: Analyze each given oxide.
\[ \mathrm{Ti_2O_3} \rightarrow \text{Ti(III) oxide, not mixed} \] \[ \mathrm{V_2O_4} = \mathrm{VO \cdot VO_2} \rightarrow \text{mixed oxide} \] \[ \mathrm{Cr_2O_3} \rightarrow \text{Cr(III) oxide, not mixed} \] \[ \mathrm{Mn_3O_4} = \mathrm{MnO \cdot Mn_2O_3} \rightarrow \text{mixed oxide} \] \[ \mathrm{Fe_3O_4} = \mathrm{FeO \cdot Fe_2O_3} \rightarrow \text{mixed oxide} \] \[ \mathrm{Fe_2O_3} \rightarrow \text{Fe(III) oxide, not mixed} \] \[ \mathrm{Co_3O_4} = \mathrm{CoO \cdot Co_2O_3} \rightarrow \text{mixed oxide} \]
Step 3: Count mixed oxides.
\[ \mathrm{V_2O_4,\ Mn_3O_4,\ Fe_3O_4} \] Total mixed oxides = \(3\)
Final Answer:
\[ \boxed{3} \]