Ortho-Nitrophenol is less soluble in water than $$p-$$ and $$m-$$ Nitrophenols because :

Nitrophenols dissolve in water mainly through hydrogen bonding between the phenolic $$-OH$$ group of the solute and the $$H_2O$$ molecules of the solvent.

For $$m$$- and $$p$$-nitrophenol, the $$-OH$$ group and the $$-NO_2$$ group are far apart on the benzene ring. Nothing blocks the $$-OH$$ hydrogen from reaching out toward water molecules. Hence strong intermolecular hydrogen bonds form with water, giving appreciable solubility.

In $$o$$-nitrophenol the $$-NO_2$$ group is adjacent (ortho) to the $$-OH$$ group. The lone pair on the phenolic oxygen and the acidic hydrogen on $$-OH$$ are so close to the $$O$$ atoms of $$-NO_2$$ that the molecule folds and forms an intramolecular hydrogen bond:

$$\overset{HO}{\underset{\large\smile}{\displaystyle\! \| \; \; NO_2}}$$

This internal H-bond “locks” the $$-OH$$ hydrogen. Because it is already satisfied internally, the $$-OH$$ cannot effectively hydrogen-bond with surrounding water molecules. As a result, fewer solute-solvent attractions arise and the solubility of $$o$$-nitrophenol drops sharply in comparison to its $$m$$- and $$p$$-isomers.

Therefore the reduced water solubility originates from the presence of intramolecular hydrogen bonding in $$o$$-nitrophenol.

Option B which is: $$o$$-Nitrophenol shows Intramolecular $$H$$-bonding