Question

Assertion (A) : Boiling point of (C₂H₅)₂NH is lower than that of n-C₄H₉NH₂.
Reason (R) : Hydrogen bonding is much more extensive in (C₂H₅)₂NH as compared to n-C₄H₉NH₂.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Same molar mass, but a primary amine has two N-H bonds and a secondary amine has one, so hydrogen bonding is more extensive in the primary amine.

Answer 1

The Correct Option is C

Step 1: Understanding the question:
We must judge two statements about amines. Both \( \mathrm{(C_2H_5)_2NH} \) and \( \mathrm{n\text{-}C_4H_9NH_2} \) have the molecular formula \( \mathrm{C_4H_{11}N} \), so they have the same molar mass. Their boiling points differ because of hydrogen bonding.

Step 2: Check the Assertion:
\( \mathrm{(C_2H_5)_2NH} \) boils near 328 K. \( \mathrm{n\text{-}C_4H_9NH_2} \) boils near 351 K.
So the boiling point of the secondary amine is lower. The Assertion is true.

Step 3: Check the Reason:
A primary amine has two N-H bonds, and a secondary amine has only one.
So \( \mathrm{n\text{-}C_4H_9NH_2} \) forms more extensive hydrogen bonds. The secondary amine also has a more branched and compact shape, with less surface contact.
The Reason says the opposite, that hydrogen bonding is more extensive in \( \mathrm{(C_2H_5)_2NH} \). The Reason is false.

Final Answer:
A is true and R is false, so the answer is option (C). \[ \boxed{\text{(C)}} \]