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, we need to identify which of the given compounds contain an aldehyde group or can be converted to one. The Tollens' test is used to distinguish aldehydes from ketones, where aldehydes give a positive result and ketones do not.

Let's analyze each compound one by one:

1. **D-Glucose**:
- D-Glucose contains an aldehyde group (CHO) at one end of its structure.
- **Conclusion**: D-Glucose gives a positive Tollens' test.

2. **D-Fructose**:
- D-Fructose is a ketose, containing a ketone group (C=O) in its structure. However, it can undergo enolization to form an aldehyde.
- **Conclusion**: D-Fructose also gives a positive Tollens' test due to enolization.

3. **CH₃CHO (Acetaldehyde)**:
- Acetaldehyde is an aldehyde (CHO) and will give a positive Tollens' test.
- **Conclusion**: CH₃CHO gives a positive Tollens' test.

4. **PhCH₂OH (Benzyl alcohol)**:
- Benzyl alcohol does not contain an aldehyde or ketone group; it is an alcohol.
- **Conclusion**: PhCH₂OH does not give a positive Tollens' test.

5. **HCOOH (Formic acid)**:
- Formic acid contains an aldehyde group (CHO) as it is the simplest carboxylic acid with an aldehyde functional group.
- **Conclusion**: HCOOH gives a positive Tollens' test.

6. **CH₃COOH (Acetic acid)**:
- Acetic acid is a carboxylic acid but does not contain an aldehyde group.
- **Conclusion**: CH₃COOH does not give a positive Tollens' test.

Now, let's summarize the results:
- D-Glucose: Positive
- D-Fructose: Positive (due to enolization)
- CH₃CHO: Positive
- PhCH₂OH: Negative
- HCOOH: Positive
- CH₃COOH: Negative

**Total Compounds Giving Positive Tollens' Test**: 4 (D-Glucose, D-Fructose, CH₃CHO, HCOOH)

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