Question

Which of the following is most acidic in nature?

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

Answer 1

Answer: (A)

$HI$

• $HF$ is the weakest acid because of it's strong $H-F$ bond.
• 
  
• Fluorine being small in size overlaps better with $1s$ orbital of hydrogen leading to a strong bond.
• 
  
• Hence can not give proton easily.Here bond strength overweighs the electronegativity of $F$.
  
• 
  
• As we go down the group, size of the halogens increases.
• 
  
• This results in poor overlap of it's orbital with $1s$ orbital of hydrogen making the $H-X$ bond weaker.
• 
  
• $H-I$ bond is the weakest of all, so it is the strongest acid.
• 
  

Therefore, option A is correct.