Strongest Acid
The strongest acid among the given options is ClO₃OH (option A).

Explanation
To determine the strongest acid, we need to consider the factors that affect acid strength. These factors include the polarity of the bond between hydrogen and the respective element, the stability of the resulting conjugate base, and the ability of the acid to donate a proton (H⁺).

Let's analyze each option individually to understand their acid strength.

Option a: ClO₃OH
- This compound, also known as chloric acid, contains a hydrogen atom bonded to a highly electronegative chlorine atom (Cl).
- The electronegativity difference between hydrogen and chlorine results in a polar bond, where the chlorine atom pulls the electron density towards itself, making the hydrogen atom more positive and easier to ionize.
- The resulting conjugate base, ClO₃⁻, is stable due to the presence of resonance in the ion.
- Chloric acid dissociates to a significant extent in water, releasing H⁺ ions, and is therefore a strong acid.

Option b: ClO₂(OH)
- This compound, also known as chlorous acid, contains a hydrogen atom bonded to a chlorine atom and an oxygen atom.
- The electronegativity difference between hydrogen and chlorine results in a polar bond, similar to chloric acid.
- However, the presence of the oxygen atom also affects the acidity.
- The resulting conjugate base, ClO₂⁻, is less stable compared to ClO₃⁻ due to the absence of resonance in the ion.
- Chlorous acid is weaker than chloric acid but still exhibits some acidity.

Option c: SO(OH)₂
- This compound, also known as sulfuric acid, contains a hydrogen atom bonded to a sulfur atom and two hydroxyl groups.
- The electronegativity difference between hydrogen and sulfur results in a polar bond, similar to chloric acid.
- The resulting conjugate base, SO₄²⁻, is highly stable due to the presence of multiple resonance structures.
- Sulfuric acid is a strong acid and is commonly used in various industrial processes.

Option d: SO₂(OH)₂
- This compound, also known as sulfurous acid, contains two hydrogen atoms bonded to a sulfur atom and two hydroxyl groups.
- The electronegativity difference between hydrogen and sulfur results in polar bonds, similar to chloric acid.
- The resulting conjugate base, SO₂(OH)₋₂, is less stable compared to SO₄²⁻ due to the absence of resonance.
- Sulfurous acid is weaker than sulfuric acid but still exhibits some acidity.

Therefore, among the given options, ClO₃OH (chloric acid) is the strongest acid due to the combination of a highly electronegative element (chlorine), polar bond, and stable conjugate base.