Chemistry Alkyl Halides UHS 2024
PMDC Verified Question 1 of 13
Identify correct ascending order of reactivity of alkyl halides:
A
Cl, Br, I, F
B
Br, I, F, Cl
C
F, Cl, Br, I
D
I, F, Cl, Br
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: F, Cl, Br, I
Concept:

The reactivity of an alkyl halide primarily depends on the bond dissociation energy of the carbon-halogen (C-X) bond.

Solution:

  • "Ascending order" means from least reactive to most reactive.
  • Reactivity is inversely proportional to bond strength. A stronger bond is harder to break, making the molecule less reactive.
  • As halogen size increases down Group 17, the C-X bond length increases, and the bond energy decreases.
  • Bond Energy Order: C-F > C-Cl > C-Br > C-I.
  • Therefore, the Reactivity Order is: R-F < R-Cl < R-Br < R-I.


Why other options are incorrect:

  • Options A, B, & D: Do not correctly reflect the inverse relationship between atomic radius/bond length and bond dissociation energy.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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