The correct answer is option 4. \(HCIO_4\).
The acidity of oxoacids generally depends on the number of oxygen atoms bonded to the central atom and the electronegativity of the central atom. In the case of chlorine oxoacids, as the number of oxygen atoms increases, the acidity tends to increase.
Let us examine each of the given oxoacids of chlorine:
1. HClO (Hypochlorous Acid):
Contains one oxygen atom bonded to chlorine.
The acidic strength is relatively low compared to the others.
2. HClO₂ (Chlorous Acid):
Contains two oxygen atoms bonded to chlorine.
More acidic than hypochlorous acid, but less acidic than acids with more oxygen atoms.
3. HClO₃ (Chloric Acid):
Contains three oxygen atoms bonded to chlorine.
More acidic than both hypochlorous acid and chlorous acid.
4. HClO₄ (Perchloric Acid):
Contains four oxygen atoms bonded to chlorine.
The most acidic among the given options.
Perchloric acid is a strong acid, and it dissociates completely in water to produce \( \text{H}^+ \) ions and \( \text{ClO}_4^- \) ions.
The trend in acidity is related to the ability of oxygen atoms to stabilize the negative charge on the conjugate base (the anion formed when the acidic hydrogen is removed). More oxygen atoms provide greater electron delocalization and stability to the resulting anion.
Therefore, the correct order of increasing acidity is \( \text{HClO} < \text{HClO}_2 < \text{HClO}_3 < \text{HClO}_4 \), and \(\text{HClO}_4\) is the most acidic among the given oxoacids of chlorine. | 
