The correct statement/s about Hydrogen bonding is/are :

A. Hydrogen bonding exists when H is covalently bonded to the highly electro negative atom.

B. Intermolecular H bonding is present in o-nitro phenol

C. Intramolecular H bonding is present in HF.

D. The magnitude of H bonding depends on the physical state of the compound.

E. H-bonding has powerful effect on the structure and properties of compounds.

Choose the correct answer from the options given below :

To determine the correct statements about hydrogen bonding, let us analyze each of the given statements one by one:

Statement A: Hydrogen bonding exists when H is covalently bonded to the highly electronegative atom.
This statement is correct. A hydrogen bond is a special type of dipole-dipole attraction that occurs when a hydrogen atom is covalently bonded to a highly electronegative atom (typically fluorine, oxygen, or nitrogen). The electronegative atom pulls the shared electron density toward itself, leaving a partial positive charge on the hydrogen atom (H^δ+), which can then attract the lone pair of a nearby electronegative atom.

Statement B: Intermolecular H bonding is present in o-nitrophenol.
This statement is incorrect. In ortho-nitrophenol (o-nitrophenol), the hydroxyl (-OH) group and the nitro (-NO₂) group are located adjacent to each other on the benzene ring. This close proximity allows the hydrogen atom of the -OH group to form a hydrogen bond with an oxygen atom of the -NO₂ group within the same molecule. Therefore, o-nitrophenol exhibits intramolecular hydrogen bonding, not intermolecular hydrogen bonding.

Statement C: Intramolecular H bonding is present in HF.
This statement is incorrect. Hydrogen fluoride (HF) is a simple diatomic molecule. Intramolecular hydrogen bonding requires the bond to form within a single molecule, which is impossible for a two-atom molecule like HF. Instead, HF molecules associate with each other via intermolecular hydrogen bonding to form zig-zag chains.

Statement D: The magnitude of H bonding depends on the physical state of the compound.
This statement is correct. The strength and extent of hydrogen bonding vary significantly with the physical state of the substance. For instance, in the solid state (like ice), hydrogen bonding is maximum and forms a rigid, ordered network. In the liquid state (like water), the hydrogen bonds are dynamic and constantly breaking and reforming. In the gaseous state, molecules are far apart, and hydrogen bonding is minimal or negligible.

Statement E: H-bonding has powerful effect on the structure and properties of compounds.
This statement is correct. Hydrogen bonding strongly influences physical properties such as melting point, boiling point, solubility, and viscosity. For example, the abnormally high boiling point of water compared to other group 16 hydrides is due to extensive intermolecular hydrogen bonding. It also dictates structural features, such as the open cage-like structure of ice and the double-helix structure of DNA.

Thus, the correct statements are A, D, and E.