A solution turns red litmus blue and phenolphthalein pink. Which could it be?
Answer and explanation
Correct answer: Sodium hydroxide solution
The governing concept is the indicator test for a base. A basic solution changes red litmus to blue and turns colourless phenolphthalein pink. Sodium hydroxide dissolves in water to give an alkaline solution, so option A satisfies both observations. Lemon juice and vinegar contain acids and would show the opposite litmus behaviour, while soda water is mildly acidic because dissolved carbon dioxide forms carbonic acid; it would not normally turn phenolphthalein pink.
Frequently asked questions
What is the correct answer to this question?
Sodium hydroxide solution
Why is this the correct answer?
The governing concept is the indicator test for a base. A basic solution changes red litmus to blue and turns colourless phenolphthalein pink. Sodium hydroxide dissolves in water to give an alkaline solution, so option A satisfies both observations. Lemon juice and vinegar contain acids and would show the opposite litmus behaviour, while soda water is mildly acidic because dissolved carbon dioxide forms carbonic acid; it would not normally turn phenolphthalein pink.
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.
