Acids do not give the characteristic reaction of `(C=O)` group because of :

Options

A. Dimerisation
B. Resonance
C. Cyclic structures
D. Attached alkyl radical

Explanation

To solve the question "Acids do not give the characteristic reaction of (C=O) group because of:", we need to analyze the structure and behavior of carboxylic acids compared to aldehydes and ketones.

### Step-by-Step Solution:

1. **Understanding the Structure of Carboxylic Acids**:
- Carboxylic acids have a functional group represented as -COOH. This group contains a carbonyl (C=O) and a hydroxyl (O-H) group.
- The carbonyl carbon is bonded to both an oxygen atom (in the carbonyl) and a hydroxyl group.

2. **Resonance in Carboxylic Acids**:
- In carboxylic acids, the lone pair of electrons on the oxygen atom of the hydroxyl group can participate in resonance with the carbonyl group.
- This results in the delocalization of electrons, leading to the formation of resonance structures.

3. **Effect of Resonance on Reactivity**:
- Due to resonance, the C=O bond in carboxylic acids does not behave like a typical carbonyl bond found in aldehydes and ketones.
- The resonance stabilizes the structure, which means that the pi electrons of the C=O bond are delocalized and do not participate in reactions as freely as they would in aldehydes and ketones.

4. **Comparison with Aldehydes and Ketones**:
- Aldehydes and ketones do not have such resonance stabilization; their C=O bonds are more reactive and can participate in characteristic reactions.
- Therefore, the presence of resonance in carboxylic acids inhibits them from undergoing the same reactions as aldehydes and ketones.

5. **Conclusion**:
- The characteristic reactions of the C=O group are not exhibited by carboxylic acids due to the resonance effect, which delocalizes the pi electrons of the C=O bond.

### Final Answer:
The correct answer to the question is **resonance**.

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