Hydrogen bonds are formed in many compounds e.g. `H_(2)O`, HF, `NH_(3)`. The boiling point of such compounds depends to a extent on the strength of hydrogen bond and the number of hydrogen bonds. The correct decreasing order of the boiling points above compounds is

Options

A. `HF gt H_(2) O gt NH_(3)`
B. `H_(2) O gt HF gt NH_(3)`
C. `NH_(3) gt HF gt H_(2)O`
D. `NH_(3) gt H_(2)O gt HF`

Answer

B

Explanation

Strength of hydrogen bonding depends on the size and electrongativity of the atom. Smaller the size of the atom, greater is the electronegativity and hence stronger is the H - bonding . Thus, the order of strength of H - bonding is `H … F gt H … O gt H ... N`. But each HF molecule is linked only to two other HF molecules while each `H_(2) O` molecule is linked to four other `H_(2)O` molecules through H - bonding .
Hence, the decreasing order of boiling points is `H_(2) O gt HF gt NH_(3)`.