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 pair of species is referred to as suboxides ?

Options

A. `CO, NO`
B. `SO_2, CaO`
C. `N_2 O, CO`
D. `N_2 O, C_3 O_2`

Answer

To determine which pair of species is referred to as suboxides, we need to analyze the definition and characteristics of suboxides based on the information provided.

### Step-by-Step Solution:

1. **Understanding Suboxides**:
- Suboxides are defined as oxides that contain a lower content of oxygen than expected. This means that in these compounds, the other element is present in excess compared to the amount of oxygen.

2. **Identifying the Options**:
- We need to look at the given pairs of species and evaluate their oxygen content relative to the other element.
- The options given are:
- A) Carbon monoxide (CO) and Nitric oxide (NO)
- B) Sulfur dioxide (SO₂) and Calcium oxide (CaO)
- C) Nitrous oxide (N₂O) and Carbon monoxide (CO)
- D) Nitrous oxide (N₂O) and C₃O₂ (tricarbon dioxide)

3. **Evaluating Each Pair**:
- **Option A**: Carbon monoxide (CO) is a normal oxide, and nitric oxide (NO) is also a normal oxide. Both have the expected amount of oxygen.
- **Option B**: Sulfur dioxide (SO₂) is a normal oxide, and calcium oxide (CaO) is also a normal oxide. Both contain the expected amount of oxygen.
- **Option C**: Nitrous oxide (N₂O) has less oxygen than expected, but carbon monoxide (CO) is a normal oxide.
- **Option D**: Nitrous oxide (N₂O) has less oxygen than expected, and C₃O₂ (tricarbon dioxide) also has a lower oxygen content compared to what would be expected from a normal oxide.

4. **Conclusion**:
- Among the options, only option D (Nitrous oxide and C₃O₂) fits the definition of suboxides because both species contain less oxygen than expected.

### Final Answer:
The pair of species referred to as suboxides is **Nitrous oxide (N₂O) and C₃O₂ (tricarbon dioxide)**.

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