A moist gas turns red litmus blue but has no effect on dry litmus. What is the most correct conclusion about the gas?
Answer and explanation
Correct answer: It forms a basic solution in moisture
Litmus changes colour because of acidic or basic species present in an aqueous medium, not simply because a dry gas touches the paper. Turning red litmus blue demonstrates a basic effect, while the absence of a change on dry litmus shows that moisture is required for the gas to dissolve, ionise, or otherwise produce the relevant basic species. The safest conclusion is therefore that the gas forms a basic solution in moisture, making option A correct. The observation does not prove that the gas is a metal or always neutral.
Frequently asked questions
What is the correct answer to this question?
It forms a basic solution in moisture
Why is this the correct answer?
Litmus changes colour because of acidic or basic species present in an aqueous medium, not simply because a dry gas touches the paper. Turning red litmus blue demonstrates a basic effect, while the absence of a change on dry litmus shows that moisture is required for the gas to dissolve, ionise, or otherwise produce the relevant basic species. The safest conclusion is therefore that the gas forms a basic solution in moisture, making option A correct. The observation does not prove that the gas is a metal or always neutral.
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.
