One solution has pH 2 and another has pH 5. Both are acidic. Which one is more likely to be more corrosive?

Correct answer: Solution with pH 2

The governing concept is the pH scale: a lower pH indicates a greater hydrogen-ion concentration and stronger acidity. A solution of pH 2 has 1,000 times the hydrogen-ion concentration of a solution of pH 5 because the difference is three pH units. Stronger acidity generally makes pH 2 more likely to be corrosive, though actual corrosiveness also depends on concentration, substance, temperature, and contact time. Therefore A is the best answer.