An aqueous solution of an unknown solute is tested with litmus paper and found to be acidic. The solution is weakly conducting compared with a solution of NaCl of the same concentration. Which of the following substances could the unknown be: KOH, \(\mathrm{NH}_{3}, \mathrm{HNO}_{3}, \mathrm{KClO}_{2}, \mathrm{H}_{3} \mathrm{PO}_{3}, \mathrm{CH}_{3} \mathrm{COCH}_{3}(\) acetone)?

First, we'll determine which of the given substances can produce acidic solutions when dissolved in water. Acids donate protons (H⁺) into the solution, resulting in a lowered pH. 1. KOH - This is a strong base, which would produce a basic solution, not acidic. 2. NH₃ - This is a weak base and can't form an acidic solution. 3. HNO₃ - This is a strong acid and can form an acidic solution. 4. KClO₂ - This is a salt, and it doesn't have any acidic protons so it cannot form an acidic solution. 5. H₃PO₃ - This is a weak acid, and it can form an acidic solution. 6. CH₃COCH₃ (acetone) - This is a neutral organic compound, and it does not form acidic solutions. From the above list, HNO₃ and H₃PO₃ are the only substances that can form acidic solutions. Now we need to analyze their conductivity properties.

Now let's analyze the conductivity of the remaining two substances: 1. HNO₃: This is a strong acid that dissociates completely in water into H⁺ and NO₃⁻ ions. This results in a high concentration of ions in the solution, which would make it a good conductor. But the unknown solution is weakly conducting, so HNO₃ cannot be the unknown substance. 2. H₃PO₃: This is a weak acid that does not completely dissociate in water. Its dissociation generates a lower concentration of ions in the solution and results in weak conductivity. This matches the description of the unknown substance. Considering both the acidic nature and conductivity, the unknown substance is likely to be: H₃PO₃ (Phosphorous acid)