Question

Assertion (A): The boiling points of alkyl halides decrease in the order: RI > RBr > RCl > RF.
Reason (R): The boiling points of alkyl chlorides, bromides and iodides are considerably higher than that of the hydrocarbon of comparable molecular mass.

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

Boiling points of alkyl halides are influenced by the size of the halogen and the intermolecular forces present.

Answer 1

The Correct Option is B

To address this question, we will examine the provided assertion and reason.

Assertion (A):
The boiling points of alkyl halides decrease in the sequence: RI > RBr > RCl > RF.

Reason (R):
The boiling points of alkyl chlorides, bromides, and iodides significantly exceed those of hydrocarbons with similar molecular masses.

1. Alkyl Halide Boiling Points:
The boiling points of alkyl halides are influenced by factors such as molecular mass, polarity, and the specific halogen present. As the halogen atom size increases down a group in the periodic table, London dispersion forces intensify. Consequently, alkyl iodides (RI) exhibit higher boiling points than alkyl bromides (RBr), alkyl chlorides (RCl), and alkyl fluorides (RF).

2. Explanation of Assertion (A):
The order of boiling points is established as RI > RBr > RCl > RF. This trend is attributed to iodine's larger atomic size, resulting in stronger dispersion forces and thus the highest boiling point. Conversely, fluorine's smaller size leads to the lowest boiling point among alkyl halides in RF.

3. Evaluation of Reason (R):
It is accurate that alkyl halides (chlorides, bromides, and iodides) possess higher boiling points than hydrocarbons of comparable molecular mass. This is due to the presence of dipole-dipole interactions and London dispersion forces between the halogen and alkyl groups, which are absent in hydrocarbons.

4. Conclusion:
Both the assertion and the reason are valid. Furthermore, the reason effectively supports the assertion, as the elevated boiling points of alkyl halides compared to hydrocarbons stem from intermolecular forces, and the observed boiling point trend aligns with the assertion.

Final Answer:
The correct choice is that both the assertion and reason are true, and the reason provides an explanation for the assertion.