Question

Mark the strongest acid.
A. $HF$
B. $HCl$
C. $HBr$
D. $HI$

Answer 1

Hint: Halogen hydrides are highly acidic. As we move from fluorine to iodine among halogens the reactivity of the halogen decreases The acidity order also follows the same trend.

Complete Step by Step Answer:
According to Bronsted acid base theory the species which can donate its hydrogen ion is called an acid and the species or compound which can donate hydroxyl ion acts as a base.
The compound which can donate hydrogen ion acts as an acid. As the hydrogen ion donating tendency of a compound increases its acidic character also increases.
As we move from hydrogen fluoride to hydrogen iodide in halogen hydrides, the size of the halogen atom that is fluorine to iodine also increases. Thus the bond of the halogen atom with hydrogen atom becomes weaker and the halogen hydride can easily release the hydrogen atom and behaves as a strong acid.
Thus among halogen hydrides hydrogen fluoride is the weakest and hydrogen iodide is the strongest halogen acid.
Thus we can write that $HI$ is the strongest acid.
Thus the correct option is D.

Note: Hydrogen bonds present in a compound make the compound weakest acid due to strong bond. Among the halogen hydrides only hydrogen fluoride contains hydrogen bonding between electronegative fluorine and electropositive hydrogen atom. It has different properties from other halogen hydrides.