Examine the following resonating structures of formic acid and arrange them in decreasing order of stability:-
`H-oversetOoverset(||)C-underset(..)overset(..)O-HharrH-overset(O^(@))overset(||)C=O_(o+)-Hharr`
`H-underset(O^(o+))underset(|)C^(o+)-underset(..)overset(..)O-HharrH-underset(..)overset(..)O-HharrH-underset(O^(o+))underset(|)C^(o+)=O-H`

Options

A. `IIgtIgtIIIgtIV`
B. `IgtIIgtIIIgtIV`
C. `IIIgtIIgtIVgtI`
D. `IVgtIIIgtIgtII`

Answer

To determine the stability of the resonating structures of formic acid, we will analyze each structure based on the following criteria: the presence of formal charges, the octet rule, and the electronegativity of the atoms carrying the charges.

### Step-by-Step Solution:

1. **Identify the Resonating Structures**:
- Structure 1: Neutral structure with no formal charges.
- Structure 2: Has a positive charge on carbon and a negative charge on oxygen.
- Structure 3: Has a negative charge on oxygen and a positive charge on carbon.
- Structure 4: Has a negative charge on carbon and a positive charge on oxygen.

2. **Evaluate Stability Based on Charge**:
- **Structure 1** is neutral, which generally makes it the most stable.
- **Structure 2** has charges, but the positive charge is on carbon (less electronegative) and the negative charge on oxygen (more electronegative), which is favorable.
- **Structure 3** has the negative charge on oxygen (more electronegative) and the positive charge on carbon, which is also favorable.
- **Structure 4** has a positive charge on oxygen (more electronegative), which is unfavorable and makes it less stable.

3. **Check for Octet Rule**:
- Structure 1 satisfies the octet rule for all atoms.
- Structure 2 also satisfies the octet rule.
- Structure 3 has all atoms satisfying the octet rule.
- Structure 4 has carbon with a negative charge, which does not satisfy the octet rule as effectively.

4. **Rank the Structures**:
- **Most Stable**: Structure 1 (neutral, all atoms have complete octets).
- **Second Stable**: Structure 2 (charges are on appropriate atoms, complete octets).
- **Third Stable**: Structure 3 (charges are on appropriate atoms, but carbon is less stable with a positive charge).
- **Least Stable**: Structure 4 (positive charge on oxygen is unfavorable).

### Final Stability Order:
1. Structure 1 (most stable)
2. Structure 2
3. Structure 3
4. Structure 4 (least stable)