A solution turns blue litmus red but does not release hydrogen when copper metal is added. What should be understood?
Answer and explanation
Correct answer: The solution may be acidic but copper is less reactive
Blue litmus turning red is a standard indication that the solution is acidic. However, hydrogen evolution depends on the reactivity of the metal as well as the acid. Metals above hydrogen in the reactivity series can usually displace hydrogen from dilute acids, whereas copper is below hydrogen and generally does not do so. Therefore option A correctly combines both observations; B and D contradict the litmus test, and C is chemically false.
Frequently asked questions
What is the correct answer to this question?
The solution may be acidic but copper is less reactive
Why is this the correct answer?
Blue litmus turning red is a standard indication that the solution is acidic. However, hydrogen evolution depends on the reactivity of the metal as well as the acid. Metals above hydrogen in the reactivity series can usually displace hydrogen from dilute acids, whereas copper is below hydrogen and generally does not do so. Therefore option A correctly combines both observations; B and D contradict the litmus test, and C is chemically false.
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.
