JEE Main levelSingle correct optionDifficulty 2 of 3cb192
The correct order of increasing strength of hydrogen bonds is
AF−H⋅⋅⋅F<O−H⋅⋅⋅O<N−H⋅⋅⋅N
BN−H⋅⋅⋅N<O−H⋅⋅⋅O<F−H⋅⋅⋅F
CN−H⋅⋅⋅N<F−H⋅⋅⋅F<O−H⋅⋅⋅O
DO−H⋅⋅⋅O<N−H⋅⋅⋅N<F−H⋅⋅⋅F
Answer: B
Hydrogen bond strength follows the electronegativity of the donor and acceptor atoms (with small size): N<O<F. Typical energies are roughly 13, 21 and 29kJmol−1. This gives N−H⋅⋅⋅N<O−H⋅⋅⋅O<F−H⋅⋅⋅F.