An unknown solution turns blue litmus red and remains colourless with phenolphthalein. Which conclusion is correct?
Answer and explanation
Correct answer: The solution is acidic
The first observation is decisive: blue litmus turns red in an acidic medium. The second observation is consistent with it because phenolphthalein is colourless in acidic solutions, whereas it becomes pink in a basic range. Together, the tests support the conclusion that the unknown solution is acidic, so option B is correct. Colourlessness with phenolphthalein alone could also occur in a neutral solution, but the litmus result rules neutrality out in this case.
Frequently asked questions
What is the correct answer to this question?
The solution is acidic
Why is this the correct answer?
The first observation is decisive: blue litmus turns red in an acidic medium. The second observation is consistent with it because phenolphthalein is colourless in acidic solutions, whereas it becomes pink in a basic range. Together, the tests support the conclusion that the unknown solution is acidic, so option B is correct. Colourlessness with phenolphthalein alone could also occur in a neutral solution, but the litmus result rules neutrality out in this case.
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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