Question

Acid strength increases in the order given as $HF < < HCl < < HBr < < HI$. As the size of the elements $F, Cl, Br, I$ increases down the group, the bond strength of $HF, HCl, HBr$ and $HI$ decreases and so the acid strength increases. In the light of the above statements, choose the correct answer from the options given below.

• A. Both Statement I and Statement II are true.
• B. Both Statement I and Statement II are false.
• C. Statement I is correct but Statement II is false.
• D. Statement I is incorrect but Statement II is true.

Answer 1

The Correct Option is A

The question assesses our understanding of the trends in acid strength within the group of hydrogen halides: HF, HCl, HBr, and HI.

1. Analyzing Statement I: 

The statement given is \(HF < < HCl < < HBr < < HI\), indicating that the acid strength increases from HF to HI. This trend is correct. As you move down the group in the periodic table, the size of the halogen atoms increases (F < Cl < Br < I). Hence, the bond strength of the hydrogen-halogen bond decreases. For example, the H-F bond in HF is a strong bond because fluorine is the smallest atom with high electronegativity, resulting in less acidic character as it does not ionize easily. On the other hand, the H-I bond in HI is weaker due to the larger size of iodine, making HI a stronger acid as it readily ionizes. Therefore, Statement I is true.

1. Analyzing Statement II:

The statement explains the reasoning behind the trend in acid strength: as the size of elements increases down the group, the bond strength decreases, leading to an increase in acid strength. This is the correct scientific rationale, as the bond dissociation enthalpy decreases with increasing atomic size, facilitating the release of hydrogen ion (H⁺) and thus, increasing the acid strength. Hence, Statement II is also true.

Considering the above analysis, both statements accurately describe the chemical behavior and provide the correct explanation for the observed trend in acid strength. Therefore, the correct answer is: Both Statement I and Statement II are true.