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 solve this question, let's analyze the assertion and reason provided.

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.

1. Boiling Points of Alkyl Halides:
In alkyl halides, the boiling points depend on several factors such as molecular mass, polarity, and the type of halogen. The size of the halogen atom increases down the group in the periodic table, which leads to an increase in London dispersion forces. This results in a higher boiling point for alkyl iodides (RI) compared to alkyl bromides (RBr), alkyl chlorides (RCl), and alkyl fluorides (RF).

2. Explanation of Assertion (A):
The order of boiling points is as follows: RI > RBr > RCl > RF. This is because iodine is the largest halogen and has the highest dispersion forces, leading to the highest boiling point. Fluorine, on the other hand, is the smallest halogen, and thus, RF has the lowest boiling point among alkyl halides.

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

4. Conclusion:
Both the assertion and the reason are correct. Moreover, the reason explains the assertion because the boiling points of alkyl halides are higher than hydrocarbons due to intermolecular forces, and the trend in boiling points follows the pattern described in the assertion.

Final Answer:
The correct option is that both the assertion and reason are true, and the reason explains the assertion.