The canonical or resonating structures of a molecule required to describe the structure of a molecule follow which of the following rules ?

Options

A. The relative position of all atoms can differ.
B. The same number of unpaired and paired electrons in all structures.
C. The energy of each structure is different.
D. Like charges are present on adjacent atoms.

Explanation

To determine the rules that govern the canonical or resonating structures of a molecule, we will analyze the given options systematically.

### Step-by-Step Solution:

1. **Understanding Resonating Structures**:
- Resonating structures are different ways of drawing the same molecule that show the delocalization of electrons. They help in understanding the actual structure of a molecule, which is a hybrid of these structures.

2. **Analyzing the Options**:
- **Option A**: "The relative position of all atoms can differ."
- This statement is not a rule for resonating structures. In canonical forms, the positions of atoms typically remain the same; only the arrangement of electrons changes.

- **Option B**: "The same number of unpaired and paired electrons in all structures."
- This option is valid. In resonating structures, the total number of electrons (both paired and unpaired) remains constant. For example, if we take a molecule like CH2=CH-CH3, the canonical forms will maintain the same number of unpaired and paired electrons across all structures.

- **Option C**: "The energy of each structure is different."
- This is not necessarily true. While some resonating structures may have different energies, others can have the same energy. The stability and energy of the resonance forms can vary, but it is not a definitive rule.

- **Option D**: "Like charges are present on adjacent atoms."
- This is generally avoided in stable resonance structures. Having like charges on adjacent atoms is not a rule and can lead to instability.

3. **Conclusion**:
- After analyzing all the options, we find that **Option B** is the correct answer. Resonating structures must maintain the same number of unpaired and paired electrons.

### Final Answer:
**Option B**: The same number of unpaired and paired electrons in all structures.