The acid strength of oxoacids depends on the number of oxygen atoms bonded to the central atom and the oxidation state of the central atom. For chlorine oxoacids, the general formula is HClO_n, where n = 0, 1, 2, 3, 4. The acid strength increases with:

1. An increase in the number of oxygen atoms (which increases the ability to stabilize the conjugate base through resonance and inductive electron withdrawal).
2. A higher oxidation state of the central chlorine atom (which makes the O-H bond more polar and easier to lose H⁺).

Let's list the chlorine oxoacids in order of increasing number of oxygen atoms and oxidation state of chlorine:

• Hypochlorous acid: HOCl (or HClO). Oxidation state of Cl = +1. Number of O atoms = 1.
• Chlorous acid: HClO₂. Oxidation state of Cl = +3. Number of O atoms = 2.
• Chloric acid: HClO₃. Oxidation state of Cl = +5. Number of O atoms = 3.
• Perchloric acid: HClO₄. Oxidation state of Cl = +7. Number of O atoms = 4.

As the number of oxygen atoms and the oxidation state increase, the acid strength increases. Therefore, the correct decreasing order of acid strength is:

$\mathrm{HClO}4>\mathrm{HClO}3>\mathrm{HClO}2>\mathrm{HOCl}$

This matches the first option.

Related Topics:

Acid Strength Trends: The strength of oxoacids is determined by the electronegativity of the central atom and the number of terminal oxygen atoms. More electronegative central atoms and a greater number of oxygen atoms (which withdraw electron density) lead to stronger acids.

Formulae:

No specific formula is used here, but the concept is based on the stability of the conjugate base. A more stable conjugate base (due to resonance and inductive effects) corresponds to a stronger acid.