Question

Which of the following hydrogen halides is most basic?

• A. $HF$
• B. $HCl$
• C. $HBr$
• D. $HI$

Answer 1

Answer: (A)

$HF$

Answer 2

The bond strength $H-X$ decreases from $HF$ to $HI$. Thus $HF$ is the most stable and hence weakest acid while is least stable and most acidic. In aqueous solutions, $HF$ is only slightly ionised but $HCl, HBr$ and $HI$ are almost completely ionised. As basicity is the reverse of acidity. Therefore, $HF$ is the most basic of all $H-X$.