The binary compounds of oxygen with other elements are called oxides. They are classified depending either upon their acid-base characteristics or on the basis of oxygen content.
(a) Normal oxides : These oxides which contain oxygen atom as permitted by the normal oxidation number, i.e., `-2` normal oxide may be acidic, basic, amphoteric or neutral.
(b) Polyoxides : The oxides which contain oxygen atoms different than those permitted by the normal oxidation number of `-2`.
(i) Peroxides : Two oxygen atoms are linked to each other and oxyegen has `-1` oxidation number. They contain `(O -O)^(2-)` unit.
(ii) Superoxodes : These oxides contain `(O-O)^(-1)` unit, i.e., each O-atom has oxidation number `-1//2`.
(c) Suboxides : These contain low content of oxygen than expected.
(d) Mixed oxides : These oxides are made of two simpler oxides.
Which of the following pairs contains mixed oxides ?

Options

A. `Pb_3 O_4, Fe_3 O_4`
B. `MnO_2, BaO_2`
C. `KO_2, Na_2 O_2`
D. `Mn_3 O_4, N_2 O_5`

Answer

To determine which pairs contain mixed oxides, we need to analyze the definitions and characteristics of mixed oxides as provided in the question. Mixed oxides are defined as oxides that are composed of two simpler oxides. Let's break down the options given in the question step by step.

### Step-by-Step Solution:

1. **Understanding Mixed Oxides**:
- Mixed oxides are formed from the combination of two different oxides. For example, if we have an oxide that can be derived from two simpler oxides, it qualifies as a mixed oxide.

2. **Analyzing the Options**:
- We need to analyze each of the given pairs to see if they can be classified as mixed oxides.

3. **Option A: Pb3O4 and Fe3O4**:
- **Pb3O4**: This oxide can be derived from the combination of PbO (lead(II) oxide) and PbO2 (lead(IV) oxide). Therefore, it is a mixed oxide.
- **Fe3O4**: This oxide is known as magnetic oxide and can be derived from FeO (iron(II) oxide) and Fe2O3 (iron(III) oxide). Thus, it is also a mixed oxide.
- **Conclusion**: Both Pb3O4 and Fe3O4 are mixed oxides.

4. **Option B: MnO2 and PaO2**:
- **MnO2**: This is manganese dioxide and is a normal oxide.
- **PaO2**: This is not a standard notation; assuming it refers to a simple oxide, it does not qualify as a mixed oxide.
- **Conclusion**: This pair does not contain mixed oxides.

5. **Option C: K2O2 and Na2O2**:
- **K2O2**: This is potassium peroxide and contains a peroxide unit.
- **Na2O2**: This is sodium peroxide, also containing a peroxide unit.
- **Conclusion**: Neither of these are mixed oxides.

6. **Option D: Mn3O4 and N2O5**:
- **Mn3O4**: This is a mixed oxide as it can be derived from MnO (manganese(II) oxide) and Mn2O3 (manganese(III) oxide).
- **N2O5**: This is nitrogen pentoxide, which is a normal oxide and does not qualify as a mixed oxide.
- **Conclusion**: This pair does not contain mixed oxides.

### Final Answer:
The only pair that contains mixed oxides is **Option A: Pb3O4 and Fe3O4**.