Which of the following compound shows negative Tollen's and Fehling's test (both) ?

Options

A. Formic acid
B. Formaldehyde
C. Benzaldehyde
D. Benzoic acid

Answer

To determine which of the given compounds shows negative results for both Tollen's and Fehling's tests, we need to analyze each compound based on their functional groups and the nature of these tests.

### Step-by-Step Solution:

1. **Understanding Tollen's Test**:
- Tollen's test is used to identify aldehydes and alpha-hydroxy ketones. A positive result is indicated by the formation of a silver mirror due to the reduction of silver ions (Ag+) to metallic silver (Ag).
- Compounds that do not have an aldehyde group or an alpha-hydroxy ketone will give a negative result.

2. **Understanding Fehling's Test**:
- Fehling's test is used to identify aldehydes that have an alpha hydrogen. A positive result is indicated by the formation of a red precipitate of copper(I) oxide (Cu2O) from the reduction of blue copper(II) ions (Cu2+).
- Compounds that do not have an aldehyde group or do not possess an alpha hydrogen will give a negative result.

3. **Analyzing the Given Compounds**:
- **Formic Acid (HCOOH)**: This compound contains a carboxylic acid group and an aldehyde group (CHO). It will show positive results for both tests.
- **Formaldehyde (HCHO)**: This is a simple aldehyde and will also show positive results for both tests.
- **Benzaldehyde (C6H5CHO)**: This compound has an aldehyde group but lacks an alpha hydrogen. It will show a positive Tollen's test but a negative Fehling's test.
- **Benzoic Acid (C6H5COOH)**: This compound is a carboxylic acid and does not have an aldehyde group. Therefore, it will show negative results for both Tollen's and Fehling's tests.

4. **Conclusion**:
- The only compound that shows negative results for both Tollen's and Fehling's tests is **Benzoic Acid (C6H5COOH)**.

### Final Answer:
The compound that shows negative Tollen's and Fehling's tests (both) is **Benzoic Acid**.