Explanation:

Intramolecular hydrogen bonding refers to the formation of hydrogen bonds within a molecule itself. It occurs when a hydrogen atom is bonded to a highly electronegative atom (such as oxygen, nitrogen, or fluorine) and forms a hydrogen bond with another electronegative atom in the same molecule.

a) o-Nitrophenol:
o-Nitrophenol consists of a phenolic group (-OH) and a nitro group (-NO2) attached to an ortho position on a benzene ring. In this molecule, hydrogen bonding occurs between the hydrogen atom of the phenolic group and the oxygen atom of the nitro group. This leads to the formation of intramolecular hydrogen bonding.

b) p-Nitrophenol:
p-Nitrophenol also consists of a phenolic group (-OH) and a nitro group (-NO2) attached to a para position on a benzene ring. However, in this molecule, hydrogen bonding occurs between the hydrogen atom of the phenolic group and the oxygen atom of another p-nitrophenol molecule (intermolecular hydrogen bonding), not within the same molecule. Therefore, p-nitrophenol does not show intramolecular hydrogen bonding.

c) Benzoic acid:
Benzoic acid consists of a carboxylic acid group (-COOH) attached to a benzene ring. In this molecule, hydrogen bonding occurs between the hydrogen atom of the carboxylic acid group and the oxygen atom of another benzoic acid molecule (intermolecular hydrogen bonding), not within the same molecule. Therefore, benzoic acid does not show intramolecular hydrogen bonding.

d) Ethanol:
Ethanol consists of an alcohol group (-OH) attached to a hydrocarbon chain. In this molecule, hydrogen bonding occurs between the hydrogen atom of the alcohol group and the oxygen atom of another ethanol molecule (intermolecular hydrogen bonding), not within the same molecule. Therefore, ethanol does not show intramolecular hydrogen bonding.

Conclusion:
Out of the given options, only o-Nitrophenol shows intramolecular hydrogen bonding. The hydrogen atom of the phenolic group forms a hydrogen bond with the oxygen atom of the nitro group within the same molecule.