Methyl orange is red and phenolphthalein is colourless in a solution. What is the nature of the solution?
Answer and explanation
Correct answer: Acidic
The governing concept is the colour response of acid–base indicators. Methyl orange is red in an acidic medium and becomes yellow in a basic medium; phenolphthalein is colourless in acidic or neutral conditions and turns pink in a basic solution. The observed combination, red methyl orange and colourless phenolphthalein, therefore indicates an acidic solution. Option C is correct. A basic solution would make phenolphthalein pink, so option A is contradicted.
Frequently asked questions
What is the correct answer to this question?
Acidic
Why is this the correct answer?
The governing concept is the colour response of acid–base indicators. Methyl orange is red in an acidic medium and becomes yellow in a basic medium; phenolphthalein is colourless in acidic or neutral conditions and turns pink in a basic solution. The observed combination, red methyl orange and colourless phenolphthalein, therefore indicates an acidic solution. Option C is correct. A basic solution would make phenolphthalein pink, so option A is contradicted.
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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