Question

The hydrogen bond is strongest in:
A. $F - H - - - O$
B. $F - H - - - F$
C. $O - H - - - S$
D. $O - H - - - N$

Answer 1

Hint: A hydrogen bond is a partial intermolecular bonding interaction between a lone pair of an electron rich atom (which has a high electron density), most commonly the second-row elements such as the nitrogen, oxygen, or fluorine, and the antibonding molecular orbital of a bond between hydrogen (H) and a more electronegative atom or group. Such an interacting system is generally denoted A–H···B, where the solid line denotes a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond.

Complete step by step answer:
The factors that affect the strength of a hydrogen bond, extensively, are electronegativity and polarity of the molecule. Let us discuss these factors one by one.
(i) Electronegativity: It is the tendency of an atom to attract a shared pair of electrons towards itself. Thus, higher the electronegativity value of an atom, the greater is its tendency to attract the bond pair of electrons as well as the electron cloud around itself. This creates a partial bond between the electronegative and the electropositive atom (that means, hydrogen).
(ii) Polarity: The greater the electronegativity difference between two atoms, the greater will be the polarity of the bond. The high electronegative atom retains a partial negative charge and the hydrogen atom attached to it retains a partial positive charge.
Among the four options provided above, the highest electronegativity is for the fluorine atom.

So, the correct answer is Option B .

Note:
 Hydrogen bond is a weak bond and is of two types. One is an intermolecular hydrogen bond which is present between two different molecules. The other one is the intramolecular hydrogen bond which is present within a molecule such as in the case of an ortho and para nitrophenol.