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

To determine the validity of the given statements regarding the strength of acids HF, HCl, HBr, and HI, let's analyze both statements separately:

1. Statement I: Acid strength increases in the order given as \(HF \ll HCl \ll HBr \ll HI\).
   • The acid strength of hydrides of halogens (HF, HCl, HBr, HI) increases as we move down the group in the periodic table.
   • Acid strength is inversely related to bond strength; weaker bonds dissociate more easily, making the acid stronger.
   • Going down the group, the size of the halogen atom increases (F < Cl < Br < I), leading to weaker H-X bonds because the bond length increases.
   • Thus, HI has the weakest bond and is the strongest acid, and HF has the strongest bond, making it the weakest acid in this group.
   • This statement is correct.
2. Statement II: 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.
   • This statement explains that the primary factor affecting acid strength in this context is the bond strength between the hydrogen atom and the halogen.
   • As the size of the halogen increases down the group, the H-X bond becomes weaker due to increased bond length, leading to easier dissociation.
   • This results in increased acid strength as the halogen size increases, precisely corroborating the stated order of increasing acid strength.
   • This statement is also correct.

Hence, the correct answer is: Both Statement I and Statement II are true.