Among the following oxides of 3d elements the number of mixed oxides are
Q. Among the following oxides of 3d elements, the number of mixed oxides are _____.

Ti2O3, V2O4, Cr2O3, Mn3O4, Fe3O4, Fe2O3, Co3O4
Correct Answer: 3

Explanation

A mixed oxide is an oxide that contains the same metal in two different oxidation states.

Now, let us analyze each oxide one by one.

Ti2O3 : Titanium is present only in +3 oxidation state. Hence, it is not a mixed oxide.

V2O4 : Vanadium is present only in +4 oxidation state. Hence, it is not a mixed oxide.

Cr2O3 : Chromium is present only in +3 oxidation state. Hence, it is not a mixed oxide.

Mn3O4 : This oxide can be written as MnO · Mn2O3. Manganese is present in +2 and +3 oxidation states. Hence, it is a mixed oxide.

Fe3O4 : This oxide can be written as FeO · Fe2O3. Iron is present in +2 and +3 oxidation states. Hence, it is a mixed oxide.

Fe2O3 : Iron is present only in +3 oxidation state. Hence, it is not a mixed oxide.

Co3O4 : This oxide can be written as CoO · Co2O3. Cobalt is present in +2 and +3 oxidation states. Hence, it is a mixed oxide.

Thus, the mixed oxides are Mn3O4, Fe3O4 and Co3O4.

Therefore, the number of mixed oxides is 3.

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