A sample turns red litmus blue but does not give carbon dioxide when acid is added. What could it be?
Answer and explanation
Correct answer: Sodium hydroxide
Turning red litmus blue shows that the sample is basic. Carbonates and hydrogen carbonates also behave as bases, but when an acid is added they release carbon dioxide, producing visible effervescence. Sodium hydroxide is a strong base and reacts with acid by neutralisation to form salt and water, without producing carbon dioxide. Thus option A fits both observations; options B-D contain carbonate or hydrogen carbonate and would give CO₂.
Frequently asked questions
What is the correct answer to this question?
Sodium hydroxide
Why is this the correct answer?
Turning red litmus blue shows that the sample is basic. Carbonates and hydrogen carbonates also behave as bases, but when an acid is added they release carbon dioxide, producing visible effervescence. Sodium hydroxide is a strong base and reacts with acid by neutralisation to form salt and water, without producing carbon dioxide. Thus option A fits both observations; options B-D contain carbonate or hydrogen carbonate and would give CO₂.
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.
