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 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:

Both statements are true, but the reason compares halides with hydrocarbons, while the assertion compares one halide with another.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
We must decide if Assertion (A) and Reason (R) are true, and then whether R explains A.

Step 2: Check Assertion (A):
In the series RF, RCl, RBr, RI the halogen gets larger and more polarisable. The van der Waals forces rise and so does the molar mass.
So the boiling points rise from RF to RI, which means they decrease in the order RI > RBr > RCl > RF. (A) is TRUE.

Step 3: Check Reason (R):
Alkyl chlorides, bromides and iodides have a polar C-X bond and a larger molar mass than a hydrocarbon of the same size.
So the dipole-dipole and van der Waals forces are stronger and their boiling points are well above the hydrocarbon. (R) is TRUE.

Step 4: Does R explain A?:
R compares a halide with a hydrocarbon. A compares one halide with another.
The order within the halides comes from the size of the halogen, not from the fact in R. So R is not the explanation of A.

Final Answer:
Both statements are true, but R does not explain A. This is option (B). \[ \boxed{\text{(B)}} \]