1. Understanding Acidity of Phenols:

Phenols are acidic due to the ability of the phenoxide ion (formed after deprotonation) to be stabilized by resonance. Substituents on the benzene ring can either increase or decrease the acidity of the phenol.

2. Effect of Substituents:

• Electron-Withdrawing Groups (EWG): EWGs (like -NO₂) increase acidity by stabilizing the phenoxide ion through resonance and inductive effects. The more effective the EWG and the closer it is to the -OH group, the greater the increase in acidity.
• Electron-Donating Groups (EDG): EDGs (like -CH₃ in cresol) decrease acidity by destabilizing the phenoxide ion.

3. Analyzing the Given Compounds:

• (I) Phenol: Base reference.
• (II) p-Cresol: The -CH₃ group is an EDG, so it will decrease the acidity compared to phenol.
• (III) m-Nitrophenol: The -NO₂ group is an EWG.
• (IV) p-Nitrophenol: The -NO₂ group is an EWG.

4. Comparing the Nitro-phenols:

Both m-Nitrophenol and p-Nitrophenol have a nitro group (-NO₂), which is an EWG. The para isomer (p-Nitrophenol) is generally more effective at stabilizing the negative charge on the phenoxide ion due to resonance effects compared to the meta isomer (m-Nitrophenol). Therefore, p-Nitrophenol is more acidic than m-Nitrophenol.

5. Ordering the Acidic Strength:

Based on the above analysis, the order of acidic strength is: p-Nitrophenol > m-Nitrophenol > Phenol > p-Cresol, which translates to IV > III > I > II.

6. Checking the Options:

The closest option to our derived order is (A) III > I > II and (B) IV > I > II. However, we know IV > III, so we need to consider the options more carefully.

Option (C) IV > I > III > II is incorrect because it places Phenol (I) between p-Nitrophenol (IV) and m-Nitrophenol (III), which is not accurate as both nitrophenols are more acidic than phenol.

Considering the options again, we need to determine the relative acidity of Phenol (I) compared to m-Nitrophenol (III). Since -NO2 is a strong EWG, even in the meta position, m-Nitrophenol (III) will be more acidic than Phenol (I). Therefore, the correct order should be IV > III > I > II.

However, none of the options perfectly match this order. The closest is option (A) III > I > II and (B) IV > I > II. Since IV is more acidic than III, we need to re-evaluate.

The correct order is IV > III > I > II. However, the options provided do not include 'I'. The question is flawed. However, if we must choose from the given options, we need to consider the relative differences. p-Nitrophenol is significantly more acidic than m-Nitrophenol. Both are significantly more acidic than p-Cresol. Therefore, the best approximation from the given options is IV > III > II.