A mixture of o-nitrophenol and p-nitrophenol can be separated by steam distillation.

Reason:

• o-Nitrophenol is steam volatile due to intramolecular hydrogen bonding, which makes it easier to vaporize with steam.
• p-Nitrophenol, on the other hand, forms intermolecular hydrogen bonding, making it less volatile and non-distillable by steam.

Thus, steam distillation effectively separates these two compounds based on their volatility differences.