Question

The correct decreasing order of the boiling points of compounds ${H_2O, HF}$ and ${NH3}$ is

• A. $\ce{HF > H_2O > NH_3 }$
• B. $\ce{H_2O > HF > NH_3 }$
• C. $\ce{NH_3 >HF > H_2O }$
• D. $\ce{NH_3 > H_2 O > HF }$

Answer 1

Answer: (B)

$\ce{H_2O > HF > NH_3 }$

Answer 2

Decreasing order of the boiling points of compounds will be, $H_2O > HF > NH_3$; due to the strength of hydrogen bonding present in given compound. So, more the hydrogen bonding, higher will be boiling point. Each water molecule can potentially form four hydrogen bonds with surrounding water molecules. Due to higher partial charge on $H$ and $F$ in $HF$, a hydrogen bond between $HF$ molecules is stronger than that of $NH_3$ molecules.
Hence, the $H_2O >HF > NH_3$ is correct.