Concept: Hydrogen Bonding

Hydrogen bonding is a special type of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom (F, O, or N). The strength of the hydrogen bond depends on the electronegativity of the atom bonded to hydrogen and the size of the atom. A higher electronegativity leads to a more polarized H-X bond, and a smaller size allows for closer approach, both contributing to stronger hydrogen bonding.

Why (B) H₂O is correct:

Among the given options, hydrogen bonding is possible in H₂O because hydrogen is bonded to oxygen, which is a highly electronegative atom (electronegativity of O = 3.44). The H-O bond is highly polar, and oxygen is relatively small, allowing for strong intermolecular hydrogen bonds.

Option Analysis:

• A) HCl: Hydrogen is bonded to chlorine (electronegativity of Cl = 3.16). While chlorine is electronegative, it is less electronegative than oxygen and larger in size, resulting in weaker or negligible hydrogen bonding compared to H₂O.
• B) H₂O: Hydrogen is bonded to oxygen (electronegativity of O = 3.44). Oxygen is highly electronegative and small, leading to strong hydrogen bonding.
• C) HI: Hydrogen is bonded to iodine (electronegativity of I = 2.66). Iodine is much less electronegative than oxygen and very large, so hydrogen bonding is not significant.
• D) H₂S: Hydrogen is bonded to sulfur (electronegativity of S = 2.58). Sulfur is less electronegative than oxygen and larger, so hydrogen bonding is very weak or negligible.

Therefore, H₂O exhibits the strongest hydrogen bonding among the given options.

Correct Answer: (B)