How many compound gives positive Tollens' test?
1. D - glucose
2. D - fructose
3. `CH_(3)overset(O)overset(||)CH`
4. `PhCH_(2)OH`
6. `HCOOH`
7. `CH_(3)COOH`

Answer

To determine how many compounds give a positive Tollens' test from the given list, we need to identify which of these compounds contain an aldehyde group, as only aldehydes can react positively with Tollens' reagent.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- 1. D-glucose
- 2. D-fructose
- 3. CH₃CHO (Acetaldehyde)
- 4. PhCH₂OH (Benzyl alcohol)
- 5. HCOOH (Formic acid)
- 6. CH₃COOH (Acetic acid)

2. **Analyze Each Compound**:
- **D-glucose**:
- Structure contains an aldehyde group (CHO) at the first carbon.
- **Result**: Positive Tollens' test.

- **D-fructose**:
- Although it is a ketose, it can undergo enolization in the presence of a base (Tollens' reagent is basic) to form an aldehyde.
- **Result**: Positive Tollens' test.

- **Acetaldehyde (CH₃CHO)**:
- Contains an aldehyde group (CHO).
- **Result**: Positive Tollens' test.

- **Benzyl alcohol (PhCH₂OH)**:
- This is an alcohol and does not contain an aldehyde group.
- **Result**: Negative Tollens' test.

- **Formic acid (HCOOH)**:
- Contains an aldehyde group (CHO) as well as a carboxylic acid group.
- **Result**: Positive Tollens' test.

- **Acetic acid (CH₃COOH)**:
- Contains a carboxylic acid group but no aldehyde group.
- **Result**: Negative Tollens' test.

3. **Count the Positive Results**:
- Compounds giving a positive Tollens' test: D-glucose, D-fructose, Acetaldehyde, Formic acid.
- Total: **4 compounds**.

### Final Answer:
**4 compounds give a positive Tollens' test.**

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