Why will the same gas change colour on moist blue indicator paper?
Answer and explanation
Correct answer: Moisture helps the gas form ions
Moisture supplies the water needed for hydrogen chloride to dissolve and ionise: HCl + H₂O → H₃O⁺ + Cl⁻. The hydronium ions give the solution acidic character, so the blue indicator changes to red. Moisture does not turn a gas into a metal, wet paper is not naturally always red, and water does not make every gas basic. Thus option A explains the observation.
Frequently asked questions
What is the correct answer to this question?
Moisture helps the gas form ions
Why is this the correct answer?
Moisture supplies the water needed for hydrogen chloride to dissolve and ionise: HCl + H₂O → H₃O⁺ + Cl⁻. The hydronium ions give the solution acidic character, so the blue indicator changes to red. Moisture does not turn a gas into a metal, wet paper is not naturally always red, and water does not make every gas basic. Thus option A explains the observation.
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.
