If a solution has pH 3 and it is made one hundred times less acidic, what will be the approximate new pH?
Answer and explanation
Correct answer: Five
The pH scale is logarithmic: pH = −log[H⁺]. A tenfold decrease in hydrogen-ion concentration raises pH by one unit. Making the solution 100 times, or 10² times, less acidic means [H⁺] becomes 100 times smaller, so the pH rises by log₁₀(100) = 2 units. Starting from pH 3, the approximate new pH is 3 + 2 = 5. Therefore option C is correct.
Frequently asked questions
What is the correct answer to this question?
Five
Why is this the correct answer?
The pH scale is logarithmic: pH = −log[H⁺]. A tenfold decrease in hydrogen-ion concentration raises pH by one unit. Making the solution 100 times, or 10² times, less acidic means [H⁺] becomes 100 times smaller, so the pH rises by log₁₀(100) = 2 units. Starting from pH 3, the approximate new pH is 3 + 2 = 5. Therefore option C is correct.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
