Question

Which acid is the strongest: HF, HCl, HBr, HI?

• A. HF
• B. HCl
• C. HBr
• D. HI

Hint:

In binary acids of the form HX, acid strength increases as the halogen size increases, with HF being the weakest and HI the strongest.

Answer 1

The Correct Option is D

Step 1: Understanding acid strength.
The strength of an acid is determined by its ability to donate a proton. In binary acids of the form HX, where X is a halogen, acid strength increases as the size of X increases, because the bond between hydrogen and the halogen becomes weaker, making it easier to release the proton.
Step 2: Explanation.
- HF (hydrofluoric acid) is the weakest acid because the bond between H and F is very strong, making it difficult to dissociate. - HI (hydroiodic acid) is the strongest acid because iodine is the largest halogen, and the bond between H and I is the weakest, making it easier to lose the proton.
Step 3: Conclusion.
Therefore, the strongest acid among the given options is HI, corresponding to option (D).

Answer 2

Step 1: For acids like HX, strength depends on how easily the H-X bond breaks to release a proton.

Step 2: As the halogen atom gets bigger (F → Cl → Br → I), the H-X bond gets weaker and breaks more easily.

Step 3: Iodine is the biggest halogen here, so HI has the weakest bond and is the strongest acid.

Step 4: So the strongest acid is HI — option (D).

Answer 3

Bond-strength comparison: The H-F bond is by far the strongest of the four, which is exactly why HF barely ionizes in water and behaves as a weak acid. Moving down to H-Cl and then H-Br, the bond keeps getting weaker and the acid keeps getting stronger. H-I has the weakest bond of the four, so it lets go of its proton the most easily, making HI the strongest acid, option (D).