If blue litmus turns red in a solution and its pH is 2, what changed when adding water makes the pH 4?
Answer and explanation
Correct answer: Acidity decreased but the solution is still acidic
The governing concept is the pH scale and dilution. Both pH 2 and pH 4 are below 7, so the solution remains acidic after water is added. Because pH increases, the hydrogen-ion concentration decreases; in fact, a two-unit rise represents a large reduction in hydrogen ions. Therefore acidity has decreased but has not disappeared, making option A correct. The other choices confuse dilution with becoming basic or claim the opposite ion change.
Frequently asked questions
What is the correct answer to this question?
Acidity decreased but the solution is still acidic
Why is this the correct answer?
The governing concept is the pH scale and dilution. Both pH 2 and pH 4 are below 7, so the solution remains acidic after water is added. Because pH increases, the hydrogen-ion concentration decreases; in fact, a two-unit rise represents a large reduction in hydrogen ions. Therefore acidity has decreased but has not disappeared, making option A correct. The other choices confuse dilution with becoming basic or claim the opposite ion change.
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.
