Q.The intramolecular hydrogen bonding in compounds leads to :

Intramolecular hydrogen bonding (chelation, e.g. in o-nitrophenol) ties up the $-OH$ and neighbouring group WITHIN one molecule, so there is little H-bonding left over either between molecules (lowering the boiling point relative to the intermolecularly-bonded isomer) or with water (lowering water solubility).

Compare o-nitrophenol and p-nitrophenol: in the ortho isomer the $-OH$ and $-NO_2$ groups are close enough to form a strong internal (intramolecular) H-bond, forming a stable 6-membered chelate ring. This 'satisfies' the H-bond-donor/acceptor capacity internally, so o-nitrophenol molecules do not associate strongly with each other (lower bp, and it is even steam-volatile) and interact only weakly with water (lower solubility). p-Nitrophenol, by contrast, c …