A student says that dry hydrogen chloride gas will turn blue litmus paper red. What is the error in this statement?
Answer and explanation
Correct answer: Dry hydrogen chloride gas has no water, so it does not change dry litmus.
The error is ignoring the need for water in showing acidity. Dry hydrogen chloride molecules do not produce hydrogen ions on dry paper, so dry blue litmus remains unchanged. When the gas dissolves in moisture, it forms an acidic solution containing H⁺ ions and turns moist blue litmus red. Therefore option A is correct; B reverses the colour change, C wrongly calls HCl neutral, and D reverses the role of bases.
Frequently asked questions
What is the correct answer to this question?
Dry hydrogen chloride gas has no water, so it does not change dry litmus.
Why is this the correct answer?
The error is ignoring the need for water in showing acidity. Dry hydrogen chloride molecules do not produce hydrogen ions on dry paper, so dry blue litmus remains unchanged. When the gas dissolves in moisture, it forms an acidic solution containing H⁺ ions and turns moist blue litmus red. Therefore option A is correct; B reverses the colour change, C wrongly calls HCl neutral, and D reverses the role of bases.
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.
