If phenolphthalein remains colourless in a solution, which conclusion is the most careful one?
Answer and explanation
Correct answer: The solution may be acidic or neutral
Phenolphthalein is an acid–base indicator that becomes pink in a sufficiently basic solution, while it remains colourless in acidic and neutral solutions. Therefore, colourlessness alone cannot prove that the solution is strongly acidic or neutral; it only rules out the usual pink basic range. Hence option B is the most careful conclusion. The other choices either reverse the indicator result or make unrelated claims.
Frequently asked questions
What is the correct answer to this question?
The solution may be acidic or neutral
Why is this the correct answer?
Phenolphthalein is an acid–base indicator that becomes pink in a sufficiently basic solution, while it remains colourless in acidic and neutral solutions. Therefore, colourlessness alone cannot prove that the solution is strongly acidic or neutral; it only rules out the usual pink basic range. Hence option B is the most careful conclusion. The other choices either reverse the indicator result or make unrelated claims.
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.
