Red litmus turns blue in a solution. Acid is added gradually, and finally both litmus papers show no change. What is the final state?
Answer and explanation
Correct answer: Neutral
The governing concept is acid–base indicators and neutralisation. A red litmus paper turning blue initially shows that the solution is basic. As acid is added, it consumes hydroxide ions and neutralises the base. When neither red nor blue litmus changes colour, the solution is at the neutral point under the stated school-level conditions. Therefore option C is correct; highly acidic or basic solutions would affect at least one indicator.
Frequently asked questions
What is the correct answer to this question?
Neutral
Why is this the correct answer?
The governing concept is acid–base indicators and neutralisation. A red litmus paper turning blue initially shows that the solution is basic. As acid is added, it consumes hydroxide ions and neutralises the base. When neither red nor blue litmus changes colour, the solution is at the neutral point under the stated school-level conditions. Therefore option C is correct; highly acidic or basic solutions would affect at least one indicator.
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.
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