Ortho and Para nitrophenols can be separated by steam distillation. This is because

o-nitrophenol undergoes intramolecular hydrogen bonding

The correct answer is Option (1) → o-nitrophenol undergoes intramolecular hydrogen bonding

Reason:

Ortho-nitrophenol (o-nitrophenol) and para-nitrophenol (p-nitrophenol) can be separated by steam distillation because of the difference in their volatility, which arises due to hydrogen bonding:

• o-Nitrophenol: The –OH and –NO₂ groups are close → forms intramolecular hydrogen bonding → Molecules exist as discrete units (no association) → Lower boiling point, steam volatile
• p-Nitrophenol: Intramolecular H-bonding is not possible → forms intermolecular hydrogen bonding → Molecules associate strongly → higher boiling point, not steam volatile

During steam distillation, o-nitrophenol distills over with steam, while p-nitrophenol remains in the flask.

Why others are incorrect:

• ☀ p-nitrophenol undergoes intramolecular hydrogen bonding → False (it undergoes intermolecular)
• ☀ o-nitrophenol undergoes intermolecular hydrogen bonding → False (it undergoes intramolecular)
• ☀ o-nitrophenol is water soluble → False (both are sparingly soluble; separation is due to volatility, not solubility)