Acetaldehyde and benzaldehyde can not be distinguished by

Options

A. Tollen's reagent
B. Fehling solution
C. Iodoform test
D. None of these

Answer

To determine which test cannot distinguish between acetaldehyde and benzaldehyde, we will analyze the reactions of both compounds with three different reagents: Tollens' reagent, Fehling's solution, and the Iodoform test.

### Step-by-Step Solution:

1. **Understanding the Compounds**:
- Acetaldehyde (CH3CHO) is an aliphatic aldehyde.
- Benzaldehyde (C6H5CHO) is an aromatic aldehyde.

2. **Tollens' Reagent Test**:
- Tollens' reagent (Ag(NH3)2+) is used to test for aldehydes.
- Both acetaldehyde and benzaldehyde react with Tollens' reagent to produce a silver mirror.
- Therefore, **both give a positive result**, and we cannot distinguish between them using this test.

3. **Fehling's Solution Test**:
- Fehling's solution is used to differentiate between aldehydes and ketones.
- Acetaldehyde reacts with Fehling's solution to produce a red precipitate of cuprous oxide (Cu2O).
- Benzaldehyde does not react with Fehling's solution and does not produce a precipitate.
- Thus, we can distinguish between acetaldehyde and benzaldehyde using this test.

4. **Iodoform Test**:
- The Iodoform test is positive for compounds that have a methyl ketone group (CH3CO-).
- Acetaldehyde contains this group and will give a positive result, forming yellow precipitate (iodoform).
- Benzaldehyde does not have this group and will not give a positive result.
- Therefore, we can also distinguish between acetaldehyde and benzaldehyde using this test.

5. **Conclusion**:
- The only test that cannot distinguish between acetaldehyde and benzaldehyde is the **Tollens' reagent test**.

### Final Answer:
Acetaldehyde and benzaldehyde cannot be distinguished by **Tollens' reagent test**.