Which of the following conditions is not correct for resonating structures?

Options

A. The contributing structures must have the same number of unpaired electrons
B. The contributing structures should have almost similar energies
C. The contributing structures should be so written that unlike charges reside on atoms that are far apart
D. The positive charge should be present on the electropositive element and the negative charge on the electronegative element

Answer

To determine which of the following conditions is not correct for resonating structures, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Resonating Structures**:
- Resonating structures are different Lewis structures that represent the same molecule. They are used when a single Lewis structure cannot fully describe the electron distribution in a molecule.

2. **Analyzing the Options**:
- **Option 1**: The contributing structures must have the same number of unpaired electrons.
- This statement is correct. For resonating structures, the number of unpaired electrons must be the same to ensure that the overall electron configuration remains consistent.

- **Option 2**: The molecular formula must be the same.
- This statement is also correct. All contributing structures must represent the same molecular formula, as they are different representations of the same molecule.

- **Option 3**: The contributing structures should be written so that the unlike charges reside on atoms that are far apart.
- This statement is **not correct**. Unlike charges can actually reside on adjacent atoms in resonating structures. For example, in some resonance forms, a positive charge can be next to a negative charge.

- **Option 4**: The positive charge should be present on the electropositive element and the negative charge on the electronegative element.
- This statement is correct. For stability reasons, it is favorable for positive charges to be on electropositive elements and negative charges on electronegative elements.

3. **Conclusion**:
- The condition that is not correct for resonating structures is **Option 3**: "The contributing structures should be so written that the unlike charges reside on the atoms that are far apart."