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Question: Answered & Verified by Expert
Affinity for hydrogen decreases in the group from fluorine to iodine. Which of the halogen acids should have highest bond dissociation enthalpy?
Chemistryp Block Elements (Group 15, 16, 17 & 18)
Options:
  • A
    $\mathrm{HF} \quad$
  • B
    $\mathrm{HCl}$
    $\begin{array}{ll}\text
  • C
    \mathrm{HBr} & \text
  • D
    \mathrm{HI}\end{array}$
Solution:
1708 Upvotes Verified Answer
The correct answer is:
$\mathrm{HF} \quad$
On moving down the group, size of halogen atom increases hence, the $\mathrm{H}-\mathrm{X}$ bond length increases. As a result, bond dissociation enthalpy decreases.
Hence, the correct order of bond enthalpy is :
$$
\mathrm{H}-\mathrm{F}>\mathrm{H}-\mathrm{Cl}>\mathrm{H}-\mathrm{Br}>\mathrm{H}-\mathrm{I} \text {. }
$$

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