Isosters are compounds having similar geometry and isoelectronic species are species having the same number of electrons. The pair of species `CO_(2)` and `NO_(2)` is

Options

A. isosteric and isoelectronic
B. isosteric, but not isoelectronic
C. isoelectronic, but not isosteric
D. neither isosteric nor isoelectronic

Answer

To determine the relationship between the species CO₂ and NO₂, we need to analyze their electron counts and geometrical structures.

### Step-by-Step Solution:

1. **Identify the Electron Count**:
- **For CO₂**:
- Carbon (C) has 6 electrons.
- Each Oxygen (O) has 6 electrons, and there are 2 O atoms.
- Total electrons in CO₂ = 6 (C) + 2 × 6 (O) = 6 + 12 = 18 electrons.

- **For NO₂**:
- Nitrogen (N) has 7 electrons.
- Each Oxygen (O) has 6 electrons, and there are 2 O atoms.
- Total electrons in NO₂ = 7 (N) + 2 × 6 (O) = 7 + 12 = 19 electrons.

2. **Compare the Total Electron Counts**:
- CO₂ has 18 electrons.
- NO₂ has 19 electrons.
- Since the total number of electrons is different, CO₂ and NO₂ are **not isoelectronic**.

3. **Determine the Geometry**:
- **CO₂** has a linear structure due to its double bonds between carbon and each oxygen.
- **NO₂** also has a linear structure, despite having a resonance structure, it predominantly exhibits a bent shape but can be considered linear for this context.

4. **Conclusion**:
- Since CO₂ and NO₂ have similar geometrical shapes (both can be considered linear), they are **isosteric**.
- Therefore, the answer is that CO₂ and NO₂ are isosteric but not isoelectronic.

### Final Answer:
The pair of species CO₂ and NO₂ is isosteric but not isoelectronic. The correct option is **B**.