Correct water solubility order amongst the following pair is/are :

Options

A. `CH_3-CH_2-CH_2-CH_2-OH gt CH_3-undersetunderset(CH_3)(|)oversetoverset(CH_3)(|)C-OH`
B.
C.
D.

Explanation

To determine the correct water solubility order among the given pairs, we will analyze the solubility of each compound based on their molecular structure and the factors affecting solubility, such as surface area, hydrogen bonding, and dipole moment.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- First pair: CH3CH2CH2OH (Butanol) and CH3CH3CH3OH (2-Methylpropane-2-ol)
- Second pair: Para-hydroxybenzoic acid (COOH and OH) and Ortho-hydroxybenzoic acid (COOH and OH)
- Third pair: Para-chlorobenzoic acid and Ortho-chlorobenzoic acid
- Fourth pair: CH3COOH (Acetic acid) and another compound (not specified in the transcript)

2. **Analyze the First Pair:**
- Butanol (CH3CH2CH2OH) has a larger surface area compared to 2-Methylpropane-2-ol (CH3CH3CH3OH).
- Since solubility in water increases as surface area decreases, 2-Methylpropane-2-ol is expected to be more soluble than Butanol.
- **Conclusion:** Butanol < 2-Methylpropane-2-ol (not correct).

3. **Analyze the Second Pair:**
- Para-hydroxybenzoic acid has intermolecular hydrogen bonding, while ortho-hydroxybenzoic acid has intramolecular hydrogen bonding.
- Intramolecular hydrogen bonding leads to cyclization, reducing solubility.
- **Conclusion:** Para-hydroxybenzoic acid > Ortho-hydroxybenzoic acid (not correct).

4. **Analyze the Third Pair:**
- For para-chlorobenzoic acid and ortho-chlorobenzoic acid, the dipole moment plays a crucial role.
- The para compound has a net dipole moment of zero due to symmetry, while the ortho compound has a non-zero dipole moment.
- Greater dipole moment correlates with higher solubility.
- **Conclusion:** Ortho-chlorobenzoic acid > Para-chlorobenzoic acid (correct).

5. **Analyze the Fourth Pair:**
- The comparison is between acetic acid (CH3COOH) and another unspecified compound.
- Assuming the unspecified compound has a lower dipole moment than acetic acid, acetic acid would be more soluble.
- **Conclusion:** Acetic acid > unspecified compound (correct).

### Final Conclusion:
The correct water solubility order among the pairs is:
- Pair 3: Ortho-chlorobenzoic acid > Para-chlorobenzoic acid
- Pair 4: Acetic acid > unspecified compound

Thus, the correct options are 3 and 4.