Question

Assertion (A): $\mathrm{HF}$ has a greater boiling point than ${\mathrm{H}}_2\mathrm{O}$.

Reason (R): $\mathrm{HF}$ has a stronger hydrogen bonding than ${\mathrm{H}}_2\mathrm{O}$.

• A. Both A and R are true and R is the correct explanation of A.
• B. Both A and R are true but R is not the correct explanation for A.
• C. A is true and R is false.
• D. A is false and R is true.

Answer 1

The correct option is D

A is false and R is true.

Explanation for Assertion:

• Water (${\mathrm{H}}_2\mathrm{O}$) has a higher boiling point than Hydrogen fluoride ($\mathrm{HF}$).
• The boiling point of ${\mathrm{H}}_2\mathrm{O}$ is $100°\mathrm{C}$ whereas the boiling point of $\mathrm{HF}$ is $19.5°\mathrm{C}$.
• Though hydrogen fluoride has a stronger hydrogen bond than water, the number of hydrogen bonds formed per molecule for water is 2 and for hydrogen fluoride, it is 1.
• Due to this boiling point of water is higher.

Thus, the given assertion is false.

Explanation for Reason:

• Hydrogen fluoride has stronger hydrogen bonding than water.
• The electronegativity of Fluorine ($\mathrm{F}$) atom is more than that of Oxygen ($\mathrm{O}$) atom which leads to stronger hydrogen bonding in hydrogen fluoride.

Thus, the given statement for reason is correct.

So, A is false and R is true.

Hence, the correct option is (D).