Question

Assertion :Boiling point of $HF$ is lesser than water. Reason: Hydrogen bonding in water is weaker than $HF$.

• A. Assertion is true, Reason is true and Reason is correct explanation for Assertion
• B. Assertion is true, Reason is true and Reason is not the correct explanation for Assertion
• C. Assertion is true, Reason is false
• D. Assertion is false, Reason is true

Answer 1

The correct option is B

Assertion is true, Reason is true and Reason is not the correct explanation for Assertion

Both $HF$ and water forms hydrogen bonds. Also the hydrogen bonds formed by water are weaker than the hydrogen bonds formed by $HF$ due to greater electronegativity difference in $HF$ than in water. Still the boiling point of $HF$ is lesser than the boiling point of water. This is because water has two hydrogen atoms. Hence, it can form two hydrogen bonds per molecule where as $HF$ has only one hydrogen atom. Hence, it can form only one hydrogen bond per molecule.
Hence, the extent of association of water is greater than the extent of association of $HF$.
Thus, Assertion is true, Reason is true and Reason is NOT the correct explanation for Assertion.