How many of the following will give 2,4-DNP test.
`1.CH_(3)CH=O " " (2) CH_(3)-overset(O)overset(||)(C)-CH_3 " " (3) Ph-CH=O " " (4) Ph-overset(O)overset(||)(C)-CH_(3)`
(5)Glucose (Aldose) (6) Fructose (Ketose) (7) HCOOH (8) Ph-NH-OH

Answer

To determine how many of the given compounds will give a positive 2,4-DNP test, we need to identify which of these compounds contain either an aldehyde or a ketone functional group, as the 2,4-DNP test is specifically used for detecting these functional groups.

### Step-by-Step Solution:

1. **Understanding the 2,4-DNP Test**:
- The 2,4-dinitrophenylhydrazine (2,4-DNP) test is used to identify aldehydes and ketones. Compounds that do not contain these functional groups, such as carboxylic acids, esters, or amides, will not give a positive test.

2. **Analyzing Each Compound**:
- **(1) CH₃CHO (Acetaldehyde)**:
- This compound contains an aldehyde group (–CHO). Therefore, it will give a positive 2,4-DNP test.
- **(2) CH₃C(=O)CH₃ (Acetone)**:
- This compound contains a ketone group (C=O). Therefore, it will also give a positive 2,4-DNP test.
- **(3) Ph-CH=O (Benzaldehyde)**:
- This compound contains an aldehyde group (–CHO). Therefore, it will give a positive 2,4-DNP test.
- **(4) PhC(=O)CH₃ (Acetophenone)**:
- This compound contains a ketone group (C=O). Therefore, it will give a positive 2,4-DNP test.
- **(5) Glucose (Aldose)**:
- Glucose has an aldehyde group, but it is in a cyclic form (pyranose) and does not have a free aldehyde. Therefore, it will not give a positive 2,4-DNP test.
- **(6) Fructose (Ketose)**:
- Fructose has a ketone group, but it is also in a cyclic form (furanose) and does not have a free ketone. Therefore, it will not give a positive 2,4-DNP test.
- **(7) HCOOH (Formic Acid)**:
- This is a carboxylic acid (–COOH) and will not give a positive 2,4-DNP test.
- **(8) Ph-NH-OH (Phenylhydroxylamine)**:
- This compound contains an –OH group and is not an aldehyde or ketone. Therefore, it will not give a positive 2,4-DNP test.

3. **Counting the Positive Results**:
- From the analysis, the compounds that give a positive 2,4-DNP test are:
- 1 (Acetaldehyde)
- 2 (Acetone)
- 3 (Benzaldehyde)
- 4 (Acetophenone)
- Thus, a total of **4 compounds** will give a positive 2,4-DNP test.

### Final Answer:
**4 compounds will give a positive 2,4-DNP test.**